For the burger: Preheat grill to medium heat. Combine seasoning, garlic salt, and pepper in a small bowl; sprinkle over both sides of patties. Grill burgers, covered, 6 minutes per side or until no longer pink in centers. Meanwhile, combine mayonnaise and lime juice. Arrange lettuce in 4 stacks; top with burgers, mayonnaise, avocado, and salsa. Wrap lettuce around burgers; serve immediately.