Preheat oven to 350°F and heat a large skillet set over medium-high heat.
Add the round beef, onion, and bell pepper. Cook until meat is no longer pink and veggies are tender.
Season with chili powder, salt, cumin, garlic powder, oregano, red pepper flakes, and pepper. Combine using a spoon until seasoning is fully incorporated and then remove from heat.
Transfer meat mixture to a 9x13 baking dish. Add the diced tomatoes, black olives and cheese and mix until well combined.
Bake for 10 minutes until cheese is fully melted and flavors are incorporated.
Top with remaining tomatoes, black olives, cheese, shredded lettuce, and serve immediately!
Best stored in an air tight container in the fridge up to 10 days. Keep fresh topping separate if you intend on storing leftovers!