Season chicken breasts with salt & pepper and cut into bite-size cubes. In a large non-stick, oven-safe skillet on med-high heat, add 1 tbsp of olive oil. Add in the chicken pieces and diced onions. After 2-3 minutes, add minced garlic and cook for another minute.
Add chicken broth, cream of chicken soup and the rice. Stir. Bring to a boil and reduce heat to medium. Cover and cook for 25-30 minutes or until rice is fully cooked. Add more chicken broth if needed. Stir a few times during cooking.
After rice has fully cooked, add the broccoli florets, chopped tomato and 1/2 cup of freshly grated sharp cheddar cheese. Stir together and cook for 2 minutes. Sprinkle the other 1/2 cup of remaining shredded cheese over the casserole. Don’t stir. Place under broiler for 1-2 minutes, until cheese is completely melted.