Heat a large skillet over medium-high heat. Add the ground beef and chopped onion and cook until the beef is browned and the onion is softened, about 4 minutes. Drain excess fat.

Stir the tomato paste into the beef mixture and cook for 1 additional minute to deepen the flavor.

Transfer the beef mixture to a large slow cooker. Add the kidney beans, crushed tomatoes, beef broth, garlic, chili powder, cumin, oregano, paprika, cinnamon (if using), and cayenne pepper (if using). Season with salt and black pepper to taste.

Cover and cook on **High for 4 hours** or **Low for 8 hours**, allowing the flavors to fully develop.

Taste and adjust seasoning if needed. Serve hot with shredded cheddar cheese, corn chips, and green onions if desired.