Begin by seasoning the chicken breasts with garlic powder, salt, and pepper on both sides.
Heat olive oil in a grill pan over medium-high heat. Grill the chicken for about 6-7 minutes per side, or until fully cooked and juices run clear. Remove from heat and let rest for a few minutes before slicing.
While the chicken is resting, mash the ripe avocado in a bowl, then mix in lime juice, cilantro, and a pinch of salt to enhance the flavor.
Preheat your oven to broil.
Assemble the sandwiches: On two slices of whole grain bread, spread a generous amount of the avocado mixture, followed by a slice of grilled chicken, a couple of slices of tomato, and a slice of mozzarella cheese.
Top with the remaining bread slices, creating two sandwiches.
Place the sandwiches on a baking sheet and broil in the oven for about 2-3 minutes, or until the cheese is melted and bubbly. Keep a close eye to prevent burning!
Once melted, remove from the oven, slice in half, and drizzle with optional hot sauce if desired.
Notes
Keep an eye on the sandwiches while broiling to prevent burning.