Heat a large skillet over medium heat. Add the ground beef and break it up with a spatula. As the beef begins to brown, add the diced onion and minced garlic. Continue cooking until the beef is fully browned and the onion is softened, about 6-8 minutes. I always take care to stir frequently so the garlic doesn’t burn and the onion becomes sweet.
Add the riced cauliflower and sliced bell peppers to the skillet with the cooked beef, onion, and garlic (from Step 1). Stir well to combine everything. Cook for about 10 minutes, stirring occasionally, until the vegetables are tender. If using frozen vegetables, make sure to cook off any extra moisture.
Pour in the chopped tomatoes and sprinkle in the ground cumin, paprika, dried oregano, cayenne pepper, and a pinch of salt. Stir everything together, making sure the spices are evenly distributed. I like to taste and adjust the cayenne for just the right level of heat.
Allow the mixture to simmer for another 5-7 minutes, stirring occasionally, until everything is heated through and the flavors have melded together. Taste and adjust the seasoning with more salt if needed.
Remove the skillet from heat. Sprinkle the chopped cilantro over the top just before serving. For a brighter flavor, I sometimes squeeze a little lime juice over the finished dish before serving.