Lay chicken breasts in a single layer in bottom of a 6 quart crock pot. Sprinkle on taco seasoning then pour in salsa. Lift chicken breast halves to get salsa underneath then cook on low for 4 hours, or high for 2 hours, or until chicken breasts shred easily with 2 forks. Shred then mix with some of the cooking liquid.
Preheat oven to 425 degrees. Add shredded chicken into the bottom of taco shells then top with shredded cheese. Bake on a foil-lined baking dish for 2-3 minutes, or until cheese is melted. Top with desired toppings.
For the Mexican Rice:
Heat oil in a pot over medium heat. Add onion, season with salt and pepper, then saute until tender, 5 minutes. Add salsa, rice, and broth then bring to a skimmer. Place a lid on top then turn the heat down to low and simmer until rice is tender, 12-15 minutes.