Heat a large skillet or Dutch oven over medium-high heat. Add the ground beef and chopped onion, then cook for 6–8 minutes while breaking the beef into small pieces, until the meat is browned and the onion is softened.

Add the minced garlic and cook for about 30 seconds, stirring constantly so it becomes fragrant without browning too much. Drain excess fat if necessary.

Stir in the undrained diced tomatoes, tomato sauce, chopped green chiles, water, chili powder, cumin, salt, and black pepper. Mix thoroughly and bring the saucy mixture to a boil.

Stir the uncooked elbow macaroni directly into the boiling mixture. Reduce the heat to low, cover the skillet, and simmer for about 12–15 minutes.

Stir every few minutes as the macaroni cooks to prevent sticking and distribute the sauce. If the mixture becomes dry before the pasta is tender, add a small splash of water.

When the macaroni is tender, remove the skillet from the heat immediately so the pasta does not become mushy. Sprinkle the cheddar cheese over the top, cover for 2–3 minutes, and serve once melted.