01 -
Season the chicken breasts with salt and pepper on both sides. Heat 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 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.