Heat a large skillet over medium heat.
Add chopped onions and garlic, sauté until translucent.
Add ground beef to the skillet, breaking it apart with a spatula.
Cook until browned, about 5-7 minutes.
Stir in diced tomatoes and chili powder.
Season with salt and pepper to taste.
Reduce heat and simmer for 10 minutes.
Sprinkle shredded cheese on top and cover until melted.
Remove from heat and let cool slightly.
Serve with optional toppings like sour cream and cilantro.