Heat a large pan over medium heat and add vegetable oil. Toss in the chopped onions, diced red bell pepper, and minced garlic. Sauté for about 10 minutes until softened and fragrant. Add chili powder, cumin, coriander, red pepper flakes, oregano, and cayenne; toast for a minute.

Increase heat to medium-high and add half of the ground beef. Break up the meat as it cooks for about 3-4 minutes until no longer pink. Transfer to slow cooker. Repeat with remaining beef.

Transfer sautéed vegetables and browned beef into the slow cooker. Stir to combine ingredients evenly.

Add drained and rinsed red kidney beans and pinto beans. Pour in diced tomatoes with juice and tomato puree. Sprinkle salt and mix until well incorporated.

Cover the slow cooker and set to cook on low for 8-9 hours or high for 4-5 hours. When ready, the chili should be thickened and aromatic.