Begin by seasoning the chicken breasts with salt and pepper. In a skillet, heat 2 tablespoons of olive oil over medium-high heat. Cook the chicken for 6–7 minutes on each side until golden brown and fully cooked, reaching an internal temperature of 165°F. Once done, take it off the heat and let it rest for a few minutes before slicing it thinly.

While the chicken rests, prepare your other ingredients. Slice the ripe avocado, cheese, and vegetables, including the red onion and tomato.

Take your chosen bread and spread a generous layer of mayonnaise on one side of each slice. Next, add a layer of Dijon mustard on top of the mayonnaise.

On half of the bread slices, start layering your sliced chicken, followed by the creamy avocado, a slice of cheese, red onion, and tomato. Top with the remaining slices of bread.

In a clean skillet, heat 1 tablespoon of butter or olive oil over medium heat. Place the sandwiches onto the skillet and grill them for 3–4 minutes on each side, pressing gently to toast the bread and melt the cheese.

Once grilled to perfection, remove the sandwiches from the skillet. Allow them to cool slightly before slicing them in half diagonally for a beautiful presentation.