1. Heat cooking spray in a large skillet over medium-high heat. Sprinkle chicken with 1/4 teaspoon pepper and salt. Sauté 3 minutes on each side or until done. Let stand 10 minutes. Slice chicken; toss with garlic.
2. Combine avocado, lime juice, mayonnaise, and bacon. Divide avocado mixture evenly among 8 bread slices. Spread 1/2 teaspoon yellow mustard over 1 side of remaining 4 bread slices. Top each mustard-topped bread slice with 1 Bibb lettuce leaf and 2 plum tomato slices; sprinkle evenly with 1/4 teaspoon black pepper. Divide half of chicken among sandwiches; top each with 1 avocado-topped bread slice. Repeat layers.