Directions

1. Combine oil, vinegar, and mustard in a small bowl. Season chicken with salt and pepper, and place in the bowl, stirring to coat. Marinate, covered, for at least a half an hour.
2. Preheat a grill or a grill pan to medium hot. Grill chicken until cooked through, 7 minutes on each side. Let cool slightly; slice thinly at an angle.
3. In a large heavy skillet over medium heat, cook bacon until crisp, and drain on paper towels. Toast bread under a broiler until lightly golden on both sides. Quarter and thinly slice avocado, and drizzle with lemon juice to prevent discoloration.
4. Assemble the sandwich in this order: bread, mayonnaise, lettuce, tomato, avocado, bread, mayonnaise, chicken, bacon, cheese, mayonnaise, bread. Serve immediately.