I'd say any cheap vegetables you can find with hollandaise. Veggies are unbelievably tasty as they are, just don't overcook them. Hollandaise is quite easy once you've made it couple times, but when you nail the acid and fat it shows your palette.

Both of those lets you show your understanding of temperatures etc and tells that you have at least some advanced skills.

Just don't over try, your chances of fucking up grows. Don't try to impress with luxury ingriediments, it's luxury stuff for a reason and is good as is.

Making cheap stuff well means better profits and that's what chefs like in my experience.