Brown ground beef and sausage in a skillet until crumbly. Drain excess fat.
Add onion and garlic; sauté 3 minutes until fragrant.
Stir in sauce, Italian seasoning, red pepper, salt, and pepper; simmer 10 minutes.
Preheat oven to 375°F and lightly grease a 9×13-inch dish.
Layer half the sauce, cheese, and pepperoni; repeat until full.
Top with mozzarella and Parmesan; cover with foil and bake 25 minutes.
Remove foil and bake 15–20 more minutes until golden.
Let rest 10 minutes before slicing; garnish with parsley.
