Whisk the flour, 1 tablespoon garlic powder, Italian seasoning, 1/2 tablespoon kosher salt, and 1/4 tablespoon pepper in a shallow bowl; set aside.
In a second shallow bowl, whisk the milk with the remaining 1/2 tablespoon garlic powder, the remaining kosher salt, and remaining 1/4 tablespoon pepper; set aside.
In a third shallow bowl, combine the Panko breadcrumbs and grated Parmesan; set aside.
Dredge each chicken breast half first in the seasoned flour, shaking off excess, then in the milk mixture, and finally press into the breadcrumb-Parmesan mixture to coat. Place coated cutlets on a parchment-lined baking sheet.
Heat 2 tablespoons of olive oil in a large skillet over medium-high until shimmering. Add chicken without crowding (work in batches) and cook until golden and releasing easily, about 4–5 minutes per side. Transfer cooked cutlets to a plate and keep warm.
Bring a large pot of water to a boil. Add the broccoli rabe and blanch for 1 minute, then drain and pat dry.
Heat 1 tablespoon olive oil in a skillet over medium heat. Sauté the blanched broccoli rabe 2–3 minutes, seasoning with salt and pepper to taste; set aside.
Stir together the mayonnaise and pesto in a small bowl.
Spread the pesto mayonnaise over both cut sides of the ciabatta. Layer provolone on the bottom half, top with the cooked chicken cutlets, then arrange roasted red peppers and the sautéed broccoli rabe over the chicken.
Close with the top half of the ciabatta and slice into individual sandwiches about 3 inches wide. Serve immediately.