Pat the chicken breasts dry and pound them to an even thickness. Season with salt and pepper and set aside.

Heat a skillet over medium heat and fry the bacon until crispy, approximately 3 minutes per side. Transfer the cooked bacon to a plate lined with paper towels, retaining the bacon fat in the skillet.

In the same skillet, cook the chicken until golden brown and the internal temperature reaches 165°F, about 6-7 minutes per side. Remove from the skillet and set aside to rest.

To assemble each sandwich, spread the mayonnaise on a slice of toasted bread. Layer with lettuce leaves and slices of tomato.

Slice the chicken and then place on top of the tomato. Top with a slice of cheddar cheese and two slices of bacon. If using avocado, place slices on top of the bacon.

Spread more mayonnaise on another slice of toasted bread and place it on top of the bacon (or avocado). Cut the sandwich in half or quarters and secure with toothpicks if desired.

Repeat with the remaining ingredients to make four sandwiches. Serve immediately and enjoy.