Step 1

Coat a casserole dish with cooking spray.

Step 2

Cook ground sirloin and sausage in a skillet over medium-low heat until browned and crumbly, stirring often, 5 to 10 minutes. Drain thoroughly. Mix in 3/4 the tomatoes, onion, butter, garlic, oregano, fennel seed, and seasoned pepper. Simmer over low heat until meat mixture comes together, about 20 minutes.

Step 3

Preheat the oven to 350 degrees F (175 degrees C).

Step 4

Fill bell peppers with meat mixture, alternating with layers of feta cheese and Parmesan cheese. Place stuffed bell peppers side-by-side in the prepared casserole dish; add remaining tomatoes around and under the peppers so they cook up and into the peppers. Sprinkle with mozzarella cheese.

Step 5

Bake in the preheated oven until browned and bubbly, about 30 minutes.