What is a good fish to substitute for chicken in this recipe?

I really want to try this sauce recipe out. The original recipe calls for Chicken, but my father refuses to let me cook chicken and cheese together…so I need a substitute for the Chicken. I was thinking a fish would work, maybe salmon? but I am unsure.

Here is the sauce recipe:
# 2 tablespoons butter
# 1 1/2 tablespoons all-purpose flour
# 1 green onion, chopped
# 3/4 cup milk
# 1 tablespoon coarse grained prepared mustard
# 3 ounces Camembert cheese, cubed
# 1 avocado – peeled, pitted and sliced

Also. How would I cook the fish for the sauce? Thank youuu