Start by browning your ground beef in a skillet over medium-high heat. Break it up with a wooden spoon as it cooks until no pink remains, then drain off any excess fat. This step ensures your soup won't be greasy.
Add all ingredients except the rice to your 6-quart crockpot. Pour in the beef broth, tomato sauce, and drained diced tomatoes, then add the browned ground beef, diced onion, both bell peppers, liquid smoke, brown sugar, minced garlic, oregano, and salt. Give everything a gentle stir to combine.
Cover the crockpot with the lid and set it to cook on high for 4 hours or low for 6 hours. The soup is done when the peppers are tender and all the flavors have melded together beautifully.
When ready to serve, stir in the cooked white rice. Add it directly to individual bowls if you're planning to store leftovers, or stir it into the entire pot if you're serving it all at once. This prevents the rice from absorbing too much liquid and becoming gummy.
Notes
Brown the beef well - Don't skip browning and draining the ground beef. This removes excess fat and develops better flavor through the caramelization process.
Don't add rice too early - Always wait until the very end to add the rice. If you cook it in the soup for the full time, it will absorb too much liquid and turn mushy.
Adjust seasoning at the end - Taste your soup before serving and add more salt, pepper, or even a splash of hot sauce if desired. The flavors develop as it cooks, so final adjustments make a big difference.
Dice peppers evenly - Cut your bell peppers into similar-sized pieces so they cook evenly. About ½-inch dice works perfectly.
Use a large enough crockpot - A 6-quart or larger slow cooker ensures you have enough room for all the ingredients without overflow.