Start by gathering all your ingredients. Dice the onion, slice the mushrooms, and mince the garlic. Have your ground turkey or chicken ready to go.
Heat the olive oil in a medium-sized, oven-safe skillet (cast iron is perfect) over medium-high heat. Add the chopped onion and cook for 2-3 minutes, until it becomes translucent and fragrant. Toss in the sliced mushrooms and cook for another 3-4 minutes, stirring occasionally, until they have softened and released their moisture. Season lightly with a pinch of salt and pepper.
Add the ground turkey or chicken to the skillet with the vegetables. Break it up with a wooden spoon and cook for 5-7 minutes, until it is fully browned and no longer pink. Stir in the minced garlic and cook for an additional 1-2 minutes, until the garlic is fragrant.
Stir in the marinara sauce and continue cooking for an additional 2-3 minutes, until the sauce is evenly distributed and the protein is fully cooked. Taste and adjust seasoning as needed.
Line the bottom of a baking dish with a layer of cooked protein mixture. Top it with a generous ladle of marinara sauce. Sprinkle the shredded mozzarella cheese evenly over the sauce and pepperoni slices. Place the baking dish in the preheated oven and bake for 10-12 minutes, until the cheese is bubbly and golden.
Serve hot with a sprinkle of fresh basil, grated Parmesan, and extra red pepper flakes.
Optional: Top with a dollop of pesto or a bit of fresh herbs for added flavor and texture.
For serving, serve with side dishes like salad or roasted vegetables for a balanced meal.