Prepare the Chicken: If using a raw chicken breast, season it with salt, pepper, and any other desired spices. Heat the olive oil in a small frying pan over a medium-high heat and cook the chicken for 6-8 minutes per side, or until cooked through. Let it rest for a few minutes before shredding or chopping it into bite-sized pieces. If you’re using pre-cooked chicken, simply shred it and have it ready.

Mash the Avocado: Cut the avocado in half, remove the stone, and scoop the flesh into a small bowl. Add the lime juice, a pinch of salt, pepper, and the optional red chilli flakes. Gently mash with a fork until it's a chunky-smooth consistency. The lime juice is crucial as it stops the avocado from browning too quickly due to a process called enzymatic browning.

Build the Sandwich: Lay out your four slices of bread. On two of the slices, evenly sprinkle half of the grated cheddar cheese. This bottom layer of cheese acts as a barrier and helps prevent the bread from getting soggy.

Layer the Fillings: Top the cheese with the shredded chicken, spreading it evenly. Next, spoon the mashed avocado over the chicken. Finally, sprinkle the remaining cheddar cheese over the avocado. Place the other two slices of bread on top to close the sandwiches.

Butter the Bread: Spread the softened butter evenly over the outer-facing sides of both sandwiches. This is what will give you that irresistible golden, crunchy crust.

Toast to Perfection: Place a large, non-stick frying pan over a medium-low heat. Carefully place the sandwiches in the pan. Cook for 4-5 minutes on the first side, until the bread is golden brown and crisp. I find that placing a lid on the pan for the first 2 minutes helps trap steam and really gets the cheese melting.

Flip and Finish: Using a spatula, carefully flip the sandwiches over. Cook for another 3-4 minutes on the second side, until it's equally golden and the cheese is completely melted and gooey.

Rest and Serve: Remove the sandwiches from the pan and let them rest on a cutting board for a minute. This allows the cheese to set just slightly, preventing it from running everywhere when you slice. Cut them in half diagonally and serve immediately.