Heat a large, heavy-bottomed skillet over medium-high heat. Add 1 tbsp olive oil. Once shimmering, add the diced onion and bell pepper (if using). Sauté until the onions are translucent and the peppers have softened, about 5 minutes.

Push the vegetables to the side of the skillet and add the 1 lb ground beef to the center. Break it up with a wooden spoon. Cook, stirring occasionally, until the beef is fully browned. Drain any excess grease from the pan.

Stir the onions and bell peppers back into the beef. Add the 2 cloves minced garlic and cook for 1 minute until fragrant.

Sprinkle in the 1 packet of taco seasoning. Stir well for another minute to wake up the spices.

Pour in the 1/2 cup of water or beef broth. Stir well, scraping up any brown bits from the bottom. Add the drained diced tomatoes and 1/2 cup salsa. Stir until cohesive and gently simmering.

Lower the heat to medium-low. Simmer uncovered for 8 to 10 minutes, letting some liquid evaporate and the sauce thicken slightly.

Turn off the heat. Sprinkle the 2 cups shredded cheese evenly over the top.

Cover the skillet tightly with a lid, or place under the broiler for 1-2 minutes until the cheese is bubbly and melted (watch carefully).

Serve immediately hot, garnished with fresh cilantro or green onions if desired, with tortillas or chips for scooping.