Dice the onion and bell pepper. Mince the garlic and keep it separate from the other vegetables because it cooks more quickly.
Heat a large skillet over medium-high heat for 1 minute. Add the ground beef and spread it into an even layer. Leave it undisturbed for 2 minutes, then break it into small pieces. Cook for 6 to 8 minutes, until no pink remains.
Push the beef to one side of the skillet. Spoon the excess grease into a heatproof bowl, leaving about 1 tablespoon in the pan.
Add the diced onion and bell pepper to the skillet. Cook over medium heat for 4 to 5 minutes, stirring often, until the onion begins to look clear and the pepper starts to soften.
Reduce the heat to medium-low. Add the garlic, chili powder, cumin, smoked paprika, oregano, and cayenne, if using. Stir constantly for 30 to 45 seconds, until fragrant. Remove the skillet from the heat before the garlic begins to brown.
Spoon the beef, vegetables, spices, and any juices from the skillet into a 6-quart slow cooker. Scrape the skillet with a rubber spatula to capture the browned bits.
Add the diced tomatoes with their juices, tomato sauce, tomato paste, beef broth, Worcestershire sauce, salt, and black pepper.
Stir until the beef is evenly distributed and no thick streaks or lumps of tomato paste remain. The uncooked chili should look dense rather than soupy.
Cover and cook on Low for 7 hours or High for 4 hours. Keep the lid closed during cooking. The chili is ready when the peppers are tender and the sauce coats the back of a spoon.
For thicker chili, remove the lid and cook on High for 20 to 30 minutes. Stir once halfway through. You may also stir in 1 additional tablespoon of tomato paste.
Taste the chili and add more salt in ¼-teaspoon amounts if needed. For more heat, add cayenne ⅛ teaspoon at a time. Ladle about 1½ cups into each bowl and add your preferred toppings.
