01 -
Season chicken breasts with salt and pepper on both sides. Heat olive oil in a skillet over medium-high heat. Cook chicken for 6-7 minutes per side until fully cooked and no longer pink in the center. Remove from heat and let rest before slicing thinly.
02 -
Slice the avocado, prepare cheese slices, slice red onion thinly, and slice tomato. 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, cheese, red onion, and tomato. Top with the remaining bread slices, mayo side down.
05 -
Heat a skillet or grill pan over medium heat. Add butter or olive oil to the pan. Cook sandwiches until bread is golden brown and cheese is melted, about 3-4 minutes per side. Press gently with a spatula to help cheese melt evenly.
06 -
Remove sandwiches from heat and let cool for a minute before slicing in half. Serve warm.