Cut the avocado in half and remove the pit. While still in the skin, slice the avocado flesh into thin even slices, about ¼ inch thick. Use a spoon to scoop out the slices carefully. Squeeze lemon juice over the avocado slices to prevent browning. Set aside while you prepare the other ingredients.

In a small bowl, combine softened butter with garlic powder and a pinch of salt. Mash together with a fork until well mixed and smooth. This garlic butter is what makes the sandwich special. Set aside.

Lay out 4 slices of bread on your work surface. Spread the garlic butter mixture evenly on one side of each bread slice. Make sure to spread it all the way to the edges for even browning. The butter should be on the outside of the sandwich.

Flip 2 bread slices over so the buttered side faces down. On the non-buttered side, layer sliced cheddar cheese evenly. Arrange avocado slices on top of the cheese in a single layer, covering the surface. Sprinkle with a pinch of salt and pepper. Add more cheese on top if you want extra melty goodness. Place the remaining bread slices on top, buttered side facing up.

Place a large skillet or griddle over medium heat. Let it warm up for about 1 minute. Do not use high heat or the bread will burn before the cheese melts. Medium heat is essential for this recipe.

Carefully place both sandwiches in the heated skillet. Cook for 3-4 minutes without pressing down hard or moving them. Let the bottom develop a golden-brown crust. You can lift a corner to check the color after 3 minutes.

Using a wide spatula, carefully flip each sandwich. The first side should be crispy and golden brown. Cook the second side for another 3-4 minutes until golden and the cheese is completely melted. You can gently press with the spatula but don't squash hard or avocado will squeeze out.

Remove sandwiches from heat when both sides are golden brown and cheese is melted. Transfer to a cutting board and let rest for 30 seconds. This brief rest allows the cheese to set slightly and makes cutting cleaner.

Using a sharp knife, cut each sandwich diagonally from corner to corner. This creates two triangular halves. Serve immediately while hot, crispy, and melty. Add optional toppings like fresh herbs, red pepper flakes, or sriracha if desired.