Add all of the ingredients for the marinade to a bowl and whisk until combined. Set aside.
Place the chicken breasts on a cutting board and cover them with plastic wrap. Pound the chicken with a meat tenderizer until they are the same thickness, about 1.5-2 inches thick.
Transfer the chicken to a pan or a gallon-sized bag and pour the marinade over the chicken. Massage the marinade into the chicken and refrigerate for at least 30 minutes or longer for more flavorful chicken.
Remove the chicken from the refrigerator and let it rest at room temperature for 10 minutes. Preheat the grill to 425ºF.
Transfer to the grill and cook the chicken for 8 minutes on the first side. Flip the chicken and place 2-3 slices of tomato on top, followed by mozzarella slices. Grill the chicken for an additional 6-8 minutes or until the internal temperature of the chicken is 165ºF.
Remove the chicken from the grill and let it rest for 5 minutes.
Top the chicken with fresh avocado, basil, onion, micro greens, and flakey salt. Serve immediately.