Season the boneless skinless chicken breasts generously with salt and pepper. Allow the chicken to sit for a few minutes while you prep the cooking equipment.

Heat a drizzle of olive oil in a skillet over medium-high heat. Once shimmering, place the seasoned chicken breasts in the skillet. Cook for 6-7 minutes on each side until they are golden brown.

Once cooked, transfer the chicken to a cutting board and let it rest for 5 minutes. Slice the chicken into thin strips for easy layering.

While the chicken rests, prep your vegetables. Slice the ripe avocado, red onion, and tomato thinly.

Spread a layer of mayonnaise and a dash of Dijon mustard on one slice of your choice of bread. Layer with sliced chicken, avocado, cheese, red onion, and tomato. Top with another slice of bread.

Grill the sandwiches in a skillet or grill pan over medium heat for about 3-4 minutes per side until golden brown.

Once both sides are golden and the cheese is gooey, remove the sandwiches from the skillet. Allow them to cool for a minute before slicing in half.