I've made this Doria vegetarian, but it's fairly easy to add shrimp, chicken or some other protein to this. When you add it, depends on how long it takes to cook. For example, if you're using chicken, you'll probably want to brown the chicken first in the pan before you saute the mushrooms (and then transfer it to a bowl while you brown the mushrooms). If you're using a fast-cooking protein such as shrimp or fish, you can probably add into the béchamel before you assemble the Doria.