**Prepare the Meat Filling:** In a large skillet over medium heat, cook the ground beef and Italian sausage until browned and fully cooked. Drain any excess grease. Add the pizza sauce, Italian seasoning, garlic powder, and mini pepperoni slices. Stir to combine and simmer for 5 minutes.
**Preheat Oven:** Preheat your oven to 375°F (190°C). Line a baking sheet with parchment paper or foil.
**Assemble the Tacos:** Place the taco shells on the prepared baking sheet. Spoon the meat filling into each shell, filling them about three-quarters full. Top each taco with a mixture of mozzarella, cheddar, and Parmesan cheese.
**Bake:** Bake the tacos in the preheated oven for 5-7 minutes, or until the cheese is melted and bubbly.
**Add Toppings:** Remove from the oven and top with your favorite optional toppings, such as olives, bell peppers, or fresh herbs.
**Serve:** Serve hot with a side of marinara sauce for dipping, if desired.