Brown the beef. Heat oil in a large pot over medium-high. Add onion and cook 3 minutes. Add ground beef, break it up, and cook 6–7 minutes until browned. Add garlic, cook 1 minute. Drain excess fat.
Season it. Add all taco seasoning directly to the beef. Stir and cook 1 minute until fragrant — this blooms the spices.
Add everything else. Pour in fire-roasted tomatoes, Rotel, black beans, pinto beans, corn, and beef broth. Stir to combine.
Simmer. Bring to a boil, then reduce to medium-low. Simmer uncovered 15–20 minutes. The longer it simmers, the better it gets.
Taste and adjust. Taste for salt and heat. Add more cayenne if you want it spicier.
Serve. Ladle into bowls. Load up the toppings — cheese, sour cream, chips, jalapeño, cilantro, lime. Serve immediately.
Notes
This soup gets better the next day — make a big batch.
Rotel + fire-roasted tomatoes = depth of flavor without extra work.
Swap ground beef for ground turkey to lighten it up.
Freezes perfectly for up to 3 months.
Storage: fridge 5 days, freezer 3 months.
Nutrition (per serving, estimated); toppings not included