Begin by placing halved boneless skinless chicken breasts in a mixing bowl. Season them generously with garlic powder, dried basil, dried oregano, salt, and coarse black pepper. Let the chicken absorb these flavors for about 10 minutes while you prepare your grill pan or stovetop grill.

Heat your grill pan over medium-high heat until it's sizzling hot, about 5 minutes. Add the seasoned chicken breasts, cooking them for approximately 3 minutes on each side until golden brown and cooked through.

In a separate skillet, drizzle a tablespoon of olive oil and set it over medium-high heat. Once hot, add halved cherry tomatoes, minced shallot, minced garlic, and a pinch of red pepper flakes. Sauté for about 5 minutes until the tomatoes blister.

Spread a generous layer of basil pesto on each grilled chicken breast and top with slices of fresh mozzarella. Return to the grill on low heat, cover with a lid for about 3 minutes until cheese melts.

Mix melted salted butter with minced garlic. Brush this mixture onto the cut sides of your Italian bread buns. Toast at 375°F for 3–5 minutes until golden.

Spread any remaining basil pesto onto the warm toasted bread. Layer on the blistered tomato relish, followed by the chicken with melted mozzarella. Top with fresh basil leaves and assemble the sandwich.