In a large skillet over medium-high heat, cook the lean ground beef and diced yellow onion for 6 to 8 minutes, breaking the meat into small crumbles with a wooden spoon, until the beef is fully browned.

Add the minced garlic and tomato paste, stirring constantly for 1 minute until fragrant.

Drain off any excess grease and transfer the mixture into the bottom of a 6-quart oval slow cooker.

To the slow cooker, add the diced red, yellow, and green bell peppers, fire-roasted diced tomatoes, crushed tomatoes, tomato sauce, low-sodium beef bone broth, Italian seasoning, smoked paprika, red pepper flakes, kosher salt, and black pepper.

Stir well until all ingredients are evenly incorporated.

Cover the slow cooker with its lid and cook on LOW for 6 to 7 hours, or on HIGH for 3 to 4 hours, until the bell peppers are fork-tender and the savory tomato-beef broth has developed deep, rich flavor.

During the final 20 to 30 minutes of cooking, gently fold in the cooked white rice so it warms through and absorbs the rich savory broth without turning mushy (alternatively, spoon cooked rice directly into individual serving bowls and ladle the hot soup over top).

Taste the soup and adjust salt or pepper as desired.

Ladle steaming generous portions into wide ceramic bowls, immediately top each bowl with a handful of freshly shredded white cheddar cheese to melt, and sprinkle with chopped fresh parsley. Serve hot alongside warm crusty sourdough bread.