Transfer chicken to gallon-size zip-top bag. Add chopped chipotle pepper, 3 tbsp. chipotle sauce, garlic, lime juice and Adobo; seal bag. Rub to coat chicken in marinade; transfer to refrigerator. Marinate at least 30 minutes, or until ready to grill.
In small bowl, stir together mayonnaise and remaining 1 tbsp. chipotle sauce until well combined; cover and set in refrigerator until ready to use.
Heat grill to medium-high heat. Add chicken to hot, greased grill grates. Grill, flipping once, until chicken is golden brown and cooked through (internal temperature registers 165°F on quick-read thermometer when inserted into thickest part of breast), about 10 minutes. Lightly toast cut sides of rolls on grill.
To assemble each sandwich, spread both cut sides of roll with 1 tbsp. reserved chipotle mayonnaise. Add chicken to bottom roll. Layer with 2 avocado slices, 2 tomato slices and 1 lettuce leaf. Replace top of roll and serve immediately.