In a skillet over medium heat, warm the olive oil and add shredded chicken, garlic powder, Italian seasoning, salt, and pepper.
Pour in the marinara sauce and stir until the chicken is fully coated. Simmer for 3–4 minutes, then remove from heat.
Lay out the sourdough slices and butter one side of each slice.
Flip the slices over and layer mozzarella cheese on half of them.
Spoon the warm chicken mixture evenly over the cheese.
Sprinkle parmesan cheese on top for extra flavor.
Cover each with another buttered slice of bread, butter-side facing out.
Heat a large skillet or griddle over medium heat and place the sandwiches onto the hot surface.
Grill each side for 3–4 minutes until golden brown and the cheese is fully melted.
Slice in half and garnish with fresh basil if desired.
