Depending on the requirements of your institution, undergraduate students may need a thesis to graduate. In some institutions, the thesis is optional, and students can chose between an exam or a thesis.
If you are a new university professor, you may give overly ambitious topics to your undergraduate thesis students. Try to place yourself in their shoes before you try to simply plug a student in one of your research projects. While I do think including undergraduate these students in research projects can be very beneficial (for the project as well as for the student), you cannot simply shove off part of your research to an undergraduate student.
I have, by now, directed a number of undergraduate thesis projects at Universidad San Francisco de Quito (12 students have graduated under my supervision), and I can share my best advice with you here on how to define a good thesis topic for an undergraduate student.
1. Case study
Given the short duration of an undergraduate thesis, a case study can be an excellent topic for a thesis. If your student is planning to go to the industry after graduation, then a case study may serve his/her needs more than a research topic. You can identify a case that fits within your current research projects to keep the outcome related to your work, but it's not a must. Again, not every student should do / wants to do / needs to do a research project for their undergraduate thesis.
2. Well-defined research project
If you do want to venture into research with an undergraduate student, and you have talked through the options very well and clearly with your student, then you may find yourself in a enjoyable position. Nothing makes me as happy as seeing how students get a first taste of research when working on their undergraduate thesis. And for some students who continue in research, they may also have forever fond memories of working on research with you for the first time in their life.
So, if your students decides to take on a research-related topic for the undergraduate thesis, then you should keep in mind that the research question should be limited. When you come fresh out of your postdoc, give your student a research topic that does not require much additional skills beyond what he/she has learned so far, and work that you could finish in about 1 month if your student has a year to work on the undergraduate thesis.
3. Consider planning
Depending on your institution, the time period available for the undergraduate thesis project ranges between a few weeks and a year. Make sure you know the requirements well before you talk with your student about your planning. Know when your student will be defending (if there is a defense), and when preliminary and final documents need to be submitted.
Then, invite your student to identify the required tasks during the thesis period, and to make a planning. When he/she has a draft list of tasks and planning, sit together, and discuss the options and feasibility of the planning - your student does not know how to plan research yet.
4. Start writing early
As the undergraduate thesis report may be one of the first pieces of academic writing of your student, make sure he/she starts writing early. Request document at the beginning of the second half of the time period for the research, and give constructive feedback to the work of your student and his/her writing. Of course, you should already have a good idea of the work itself (I meet weekly for 30' with my thesis students to discuss progress), but it is in writing that certain things may capture your attention, and where you may find parts of the work that need strengthening.
5. Involve students in research before the final semester
If your institution only gives one semester or quarter for the undergraduate research project, you can invite students to work with you on a research-related topic already before the final semester. For some of the more extensive projects that I have worked on with my students, I have worked with them for up to 1,5 years. I invite them to see if they are interested in research in the first place, and if so, I try to work with them for a slightly longer amount of time. My goal here is not to overload students in terms of workload, but if we want to do experimental work, for example, the time it takes to import instrumentation is often very long, so that experiments are simply not an option for a 1-semester project. If we start to work earlier, we may be able to do something fun in the lab.
6. Consider their career plans
I've mentioned this advice already before: always talk with your student about their interests and their career plans. Our work as university professors is not to have a battalion of minions doing our research work for us. Our work is to guide young people on their career path: finding their interest and helping them sort out what they want to do after graduation. Don't limit your possible topics to elements of your research. Try to broaden your horizon and open up to a larger variety of topics.
I have published with my undergraduate students: conference papers, and I have a few papers in review of which the first author is a former undergraduate student. Publishing certainly is not a must. But if your student is interested in continuing studies after the undergrad years, then why not? Again, make sure your student understands the expectation and the extra workload this implies. And on your side, make sure you understand that you will need to teach your students how to write a paper. If both are clear on the expectations, then you can discuss if you should pursue this option.