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 through with no pink remaining. Remove from heat and let rest for a few minutes before slicing thinly.
02 -
Slice the avocado, tomato, and red onion. Arrange the cheese slices for easy assembly.
03 -
Combine mayonnaise and Dijon mustard, then spread evenly on one side of each bread slice.
04 -
On two bread slices (spread-side up), layer the sliced chicken, avocado, cheese, red onion, and tomato. Top with the remaining bread slices, spread-side down.
05 -
Heat butter or olive oil in a skillet over medium heat. Place assembled sandwiches in the skillet and cook for 3-4 minutes per side, gently pressing with a spatula. Cook until bread is golden brown and cheese is fully melted.
06 -
Remove sandwiches from the skillet, let cool slightly, then slice diagonally in half. Serve warm.