In a small bowl, combine the shredded or diced cooked chicken breast with garlic powder, smoked paprika, a pinch of salt, and a pinch of black pepper. Mix well until the chicken is evenly coated with the seasonings. Set aside.

In another small bowl, mash the pitted and scooped avocado with a fork until you reach your desired consistency (chunky or smooth). Stir in the fresh lime juice, 1/4 tsp salt, and 1/8 tsp black pepper. If using, fold in the finely chopped fresh cilantro.

Lay out the four slices of sourdough bread. Spread 1/2 tablespoon of mayonnaise evenly on one side of each bread slice.

On two of the bread slices (mayonnaise-side up), layer half of the seasoned chicken mixture. Top with two slices of provolone cheese, then half of the creamy avocado mash, and finally a few slices of ripe tomato.

Place the remaining two bread slices (mayonnaise-side down) on top to complete the sandwiches, ensuring the mayonnaise side will be buttered and grilled.

Heat a large skillet or frying pan over medium heat. Evenly spread 1 tablespoon of softened unsalted butter on the outside of each assembled sandwich.

Carefully place the sandwiches, butter-side down, into the hot skillet. Cook for 3-5 minutes per side, or until the bread is golden brown and crispy, and the cheese is thoroughly melted and gooey. You may need to press down gently with a spatula to ensure even contact and better melting.

Carefully remove the grilled sandwiches from the skillet. Cut each sandwich in half diagonally and serve immediately. Enjoy your gourmet Chicken Avocado Melt Sandwich!