Preheat the oven. Set to 375°F (190°C). Lightly grease a 9x13-inch baking dish.

Cook the vegetables. Heat 1 tablespoon olive oil in a large skillet over medium-high heat. Add onions and peppers with a pinch of salt. Cook 6–8 minutes until softened and lightly browned. Add mushrooms and cook 3–4 minutes more. Stir in garlic for 30 seconds. Transfer veggies to a bowl.

Brown the beef. In the same skillet, heat the remaining 1 tablespoon oil. Add ground beef, breaking it up as it cooks. Season with salt, pepper, paprika, and Worcestershire. Cook until browned with no pink left, about 5–7 minutes. Drain excess fat if needed.

Make the creamy binder. In a small bowl, whisk cream cheese, Greek yogurt, and Dijon until smooth. This mixture helps the casserole set while staying moist.

Combine the filling. Return the veggies to the skillet with the beef. Fold in the cream cheese mixture until evenly coated. Taste and adjust seasoning—add a pinch of salt or a splash more Worcestershire if you like.

Layer the casserole. Spread the beef-and-veg mixture into the baking dish. Top with half the provolone and half the mozzarella. Give it a gentle toss to distribute, then finish with the remaining cheese in an even layer.

Bake. Place on the center rack and bake 15–18 minutes, until the cheese is melted and bubbly around the edges.

Rest and garnish. Let it sit 5 minutes to set. Sprinkle with chopped parsley. Slice into squares and serve.

Optional serving ideas. Spoon over cauliflower rice for lower carbs, over quinoa for extra protein and fiber, or into toasted hoagie rolls if you want the classic sandwich vibe.