Step 1

Cutting against the grain, slice steak into thin strips then cut slices into ½” pieces.

Step 2

Preheat oven to 400 degrees and spray 9×13-inch baking dish with nonstick cooking spray.

Step 3

In a large skillet over medium heat, melt butter. Add minced garlic and heat until fragrant, about 1 minute. Add sliced steak and cook until browned. Transfer cooked steak to plate or bowl and set aside. Discard liquid from pan.

Step 4

To same skillet over medium-high heat, add peppers, mushrooms, and onions and cook until vegetables are tender and liquid has evaporated, about 5-7 minutes. Remove skillet from heat. Set aside.

Step 5

To a mixing bowl, add egg, shredded mozzarella, cream cheese, pepper, and salt and, using an electric mixer, mix until well combined. Stir in cooked steak and vegetables.

Step 6

Transfer mixture into prepared baking dish and arrange provolone cheese slices in an even layer atop mixture. Transfer dish to middle oven rack to bake until edges of casserole are golden brown and bubbling, about 25 minutes.

Step 7

Remove baking dish from oven and allow casserole to cool for at least 10 minutes before slicing and serving.