Structure your answer around the Double Diamond: Discover, Define, Develop, Deliver. Show where users were involved at each stage.
Strong answers show a complete process: discovery (user research, stakeholder interviews), definition (personas, user stories, problem statements), ideation (sketching, wireframing), prototyping, testing (usability tests), iteration, and handoff to engineering. Look for evidence of user involvement throughout, not just at the end.
Baseline question to understand the candidate's design maturity. Weak candidates jump straight to visual design. Strong candidates start with understanding the problem.