In a bowl, whisk together soy sauce, pineapple juice, brown sugar, olive oil, garlic powder, and black pepper.
Place chicken breasts in a large resealable bag or container and pour the marinade over them. Marinate for at least 2 hours or overnight.
Preheat the grill to medium-high heat. Remove chicken from marinade and grill for 5-6 minutes per side or until fully cooked.
During the last few minutes of grilling, place pineapple rings on the grill and cook until lightly charred.
Top each chicken breast with a slice of mozzarella cheese and let it melt slightly on the grill.
Toast sandwich buns on the grill if desired.
Assemble sandwiches by placing lettuce on the bun bottom, followed by grilled chicken with melted cheese, grilled pineapple, and any sauce of choice. Top with the bun and serve.