Preheat your oven to 375°F (190°C) and grease a baking dish with non-stick spray or olive oil.

Slice off the tops of the bell peppers, remove the seeds and membranes, and place them cut side up in the baking dish.

Heat olive oil in a pan over medium heat, add diced onions, and sauté for about 4-5 minutes until translucent.

Add ground beef to the onions and cook for 6-8 minutes until browned; stir in taco seasoning and diced tomatoes for one minute.

Stir in cauliflower rice and shredded cheese into the beef mixture until thoroughly combined.

Fill the bell peppers with the beef filling, heap it above the edges, and sprinkle remaining cheese on top.

Bake for 20-25 minutes, until the cheese is melted and bubbly, and the peppers are tender.

Let cool for a few minutes before serving; garnish with sour cream, cilantro, and jalapeños if desired.