Place the trimmed boneless, skinless chicken breasts into a large bowl.
Pour the remaining ingredients, except for the salt, black pepper and cayenne pepper, over the top of the chicken.
Stir until all of the sauce ingredients are fully submerged into the chicken thigh pieces.
Cover and refrigerate for 2 hours.
Remove the bowl from the fridge and let come down to room temperature for 15 minutes.
Add a small amount of salt, black pepper and cayenne pepper to taste. Use the most restraint with the salt because both the gluten free soy and Worcestershire sauces have salt in them. But, since the salts in the packaged sauces hit your tongue on different places than table salt, you may want to add just a bit to balance out the salt flavors.
Preheat grill to medium-high heat.
When the grill is ready, remove the garlic slices from the bowl.
Transfer the marinated boneless, skinless chicken thighs from the bowl to the grill, shaking off excess marinade before each transfer, if necessary.
Grill for 4 to 5 minutes per side, using a digital thermometer to ensure that each chicken thigh reads 165 degrees F before removing from the grill.