Step 1

Preheat oven to 350 degrees F (175 degrees C). Grease a 3-quart baking dish.

Step 2

Heat olive oil in a large skillet over medium heat; cook and stir mushrooms, onion, and bell pepper in hot oil until onions are translucent, about 5 minutes. Transfer vegetables to a large bowl.

Step 3

Stir hash brown potatoes, ham, cream of chicken soup, sour cream, about 3/4 cup Cheddar cheese, and about 3/4 cup Parmesan cheese into vegetables. Spread potato mixture into the prepared baking dish. Sprinkle remaining 1/4 cup Cheddar cheese and 1/4 cup Parmesan cheese over potato mixture.

Step 4

Bake in the preheated oven until bubbly and cheese is melted, 40 to 45 minutes. Let stand for 5 minutes before serving.