Brown the Beef & Onion: Heat a large skillet over medium-high. Add the onion, ground beef, break it up, and cook until browned. Drain the excess fat and add beef to your slow cooker.
Add the Good Stuff: Toss in the kidney beans, diced tomatoes, and spices. Stir it all together until combined.
Slow Cook Magic: Set your slow cooker to Low for 6–8 hours, or High for 3–4 hours. The longer it simmers, the richer the flavors.
Serve It Up: Ladle into bowls and top with your favorites: shredded cheese, sour cream, green onions, or crushed tortilla chips.