Lightly butter and toast the sourdough roll pieces in a skillet for 2-3 minutes before topping the casserole; this prevents them from becoming soggy and creates a golden, crispy texture that holds up during baking.

Cook the mushrooms in butter over medium-high heat until golden and their moisture evaporates before adding to the casserole; this concentrates their umami flavor and prevents a watery dish.

After sautéing the onions and peppers, deglaze the pan with white wine to lift flavorful browned bits, then reduce by half before combining with the cream of mushroom soup for a richer, more complex sauce.

Distribute chicken pieces evenly throughout the casserole dish rather than clumping them together; this ensures every piece cooks evenly and absorbs the creamy sauce throughout baking.

Mix half the Parmesan into the cream sauce base and sprinkle the remainder over the sourdough topping before baking; this creates a savory depth in the filling while achieving a golden, crispy cheese crust on top.