Crockpot Chicken Fajitas

Place chicken into a slow-cooker and season with cumin, chili powder, garlic powder, red pepper flakes, and salt and pepper. Top with bell peppers, onions, and diced tomatoes. Cook on low for 4 to 6 hours, or until chicken is cooked through.  Remove chicken from slow-cooker and slice into strips. Use a slotted spoon to remove peppers, onions, and tomatoes and place on a plate with sliced chicken. Discard liquid.  Serve fajitas in tortillas with desired toppings.