Heat olive oil in a skillet over medium heat. Season the chicken breast with garlic powder, paprika, salt, and black pepper. Cook for 5–6 minutes per side until fully cooked. Let it rest, then slice or shred.
In a bowl, mash the avocado with lime juice, salt, pepper, and chopped herbs. Mix until creamy with a little texture remaining.
Butter one side of each bread slice. Turn the slices over and layer cheese, chicken, avocado spread, and more cheese.
Top with the second bread slice, keeping the buttered side facing outward.
Heat a skillet over medium-low heat. Grill the Chicken Avocado Melt Sandwich for 3–4 minutes per side, pressing lightly with a spatula.
Cook until the bread becomes golden and crispy and the cheese melts completely.
Slice in half, garnish with fresh herbs, and serve warm with an optional squeeze of lime.