01 -
Season the chicken breasts with salt and pepper on both sides. Heat the olive oil in a skillet over medium-high heat. Cook the chicken breasts for 6–7 minutes on each side, or until fully cooked and no longer pink in the center. Remove from the skillet and let rest for a few minutes before slicing thinly.
02 -
Slice the avocado and prepare the cheese slices. Set them aside.
03 -
Spread a thin layer of mayonnaise and Dijon mustard on each slice of bread.
04 -
On two slices of bread, layer the sliced chicken, avocado, and cheese. Add a few slices of red onion and tomato on top. Top each sandwich with the remaining slices of bread, mayo side down.
05 -
Heat a skillet or grill pan over medium heat. Add a bit of butter or olive oil to the pan. Place the sandwiches in the skillet and cook until the bread is golden brown and the cheese is melted, about 3–4 minutes per side. Press down gently with a spatula to help the cheese melt evenly.
06 -
Remove the sandwiches from the skillet and let them cool for a minute before slicing in half. Serve warm.