Cut the avocado in half and remove the pit. Scoop the flesh into a bowl. Add lemon juice, salt and black pepper. Mash gently with a spoon. Keep it creamy, not too smooth.

If your chicken is cold, warm it slightly. Slice the chicken into thin pieces. Season lightly with salt and pepper. This helps bring out the flavor when heated.

Lay the bread slices on a board. Spread mayonnaise on one side of each slice. On the other side, spread the mashed avocado evenly. This creates a creamy base.

Place sliced chicken over the avocado layer. Add cheese slices on top of the chicken. Cover with the second bread slice, mayo side facing out.

Place a skillet on medium heat. Add butter and let it melt slowly. Make sure the pan is evenly coated. This helps the bread turn golden.

Place the sandwich in the pan. Cook for about three to four minutes per side. Press gently with a spatula. Flip when golden brown and cheese starts melting.

Remove the sandwich from the pan. Let it rest for one minute. Cut in half and serve warm. Enjoy the gooey cheese and creamy avocado.