Preheat your oven to 400°F (200°C). Line a large baking sheet with parchment paper or lightly grease it for easy cleanup.
In a mixing bowl, combine the ground beef or turkey with taco seasoning. Mix well until the meat is evenly coated with the seasoning.
Spread the seasoned meat evenly on one side of the baking sheet.
On the other side of the baking sheet, arrange the diced bell peppers, diced onion, corn, and black beans. Drizzle with olive oil and season with salt and pepper. Mix to coat evenly.
Place the baking sheet in the preheated oven and bake for 15 minutes.
After 15 minutes, remove the baking sheet, stir the meat and veggies together, and sprinkle shredded cheese over the top.
Return to the oven and bake for an additional 5 minutes or until the cheese is melted and bubbly.
Remove from the oven, and let it cool slightly. Warm the tortillas in a separate skillet or microwave.
To serve, spoon the meat and vegetable mixture into each tortilla, top with avocado slices, salsa, and fresh cilantro if desired.