Sprinkle 1 tbsp Weber® Steak 'n Chop Seasoning over both sides of chicken breasts. Grill chicken over Direct High heat, with the lid closed as much as possible, for 6 to 8 minutes until browned.
Turn and grill an additional 6 to 8 minutes until chicken is cooked through and internal temperature is at least 170°F. Remove chicken from grill and let rest 5 minutes.
While chicken is cooking, combine mayonnaise, Member’s Mark™ Parsley and Weber® Steak 'n Chop Seasoning in a small bowl; set aside.
Toast buns over Direct High heat for 1 minute, until lightly toasted and browned. Place chicken on bun and top with a slice of cheese. Spread flavored mayonnaise on top bun half. Add 2 slices bacon, a slice of tomato and 2 slices avocado to each sandwich. Serve immediately.