Brown the ground chuck and garlic in a pot over medium-high heat.
Add tomato sauce, Ro-tel, salt, oregano, cumin, and chili powder. Cover and simmer on low for 30 minutes.
Stir in the beans, cover, and simmer for another 20 minutes.
Mix masa with warm water, then add to the chili. Stir and simmer for 10–15 minutes.
Slice Frito bags open lengthwise.
Fill with chili, cheese, and diced onion (if using). Serve immediately!