Place chicken breasts in a slow cooker and season with cumin, garlic salt, chili powder, and black pepper. Add diced tomatoes and cook on low for 6-8 hours or high for 4-6 hours until tender, then shred.

Bring a large pot of water to a boil and add bell peppers. Boil for 5 minutes until just tender. Remove and cool slightly. Carve jack-o-lantern faces if desired.

In a bowl, combine cooked Mexican rice, shredded chicken, black beans, and cheddar cheese. Stir until well mixed.

Preheat your oven to 350°F (175°C). Stuff each pepper with the chicken and rice mixture, fill gently, top with cheese, and place in a baking dish. Bake for 30 minutes.

Remove from the oven, cool for a few minutes, and serve warm with a side salad or mini quesadillas.