Mix together the olive oil, garlic, chili powder, cumin, paprika, salt, and black pepper to make a marinade.

Place the chicken breasts in a large resealable bag and pour the marinade over the chicken. Massage the marinade into the chicken to make sure it is evenly coated.

Refrigerate the chicken for at least 30 minutes, or up to 24 hours. This will allow the flavors of the marinade to penetrate the chicken and give it a flavorful, juicy taste.

Preheat your grill or oven to 375°F. If you are using a grill, lightly oil the grates to prevent the chicken from sticking.

Remove the chicken from the marinade and discard any remaining marinade. Grill or roast the chicken for 20-25 minutes, or until it is cooked through and reaches an internal temperature of 165°F.

While the chicken is cooking, heat a large pan over medium heat and add the tomato sauce, onions, bell peppers, and diced tomatoes. Cook until the vegetables are tender, about 5-7 minutes.

Once the chicken is cooked, slice it into thin strips and add it to the pan with the sauce and vegetables. Stir to combine and cook for an additional 5 minutes.