Lead with pragmatism: "I would not rewrite it. I would add tests around the most critical paths, extract business logic into classes, and modernise module by module while shipping features."
Best answers describe a pragmatic, incremental approach: add characterisation tests first, then extract logic from templates, introduce autoloading, wrap global state in injectable services, and migrate one module at a time. Strong candidates discuss the Strangler Fig pattern, setting up CI early, and resisting the urge to rewrite from scratch. They balance technical debt reduction with delivering business value.
Tests real-world maturity. Junior developers often want to rewrite everything. Seniors know that incremental modernisation is safer and more sustainable. Ask what they would do first and why.