Place the chicken on a baking sheet and bake for 20 minutes or until fully cooked.
While the chicken is baking, prepare the guacamole. In a mixing bowl, mash the avocados and mix in lime juice, diced tomato, red onion, minced garlic, salt, and pepper.
Once the chicken is cooked, remove it from the oven and top each piece with a generous amount of guacamole and shredded cheese.
Return the chicken to the oven and bake for an additional 5 minutes or until the cheese is melted and bubbly.