I slice each chicken breast in half horizontally so they’re thinner and cook through more evenly. I season both sides with salt, pepper and garlic powder. Then I heat a grill or sauté pan with a little olive oil and cook until done and slightly golden.
While the chicken rests, I brush the inside of each roll with olive oil, place them oil-side down on the hot grill (or in the pan), and toast just until the surface is crisp and lightly browned. This step is essential to avoid a soggy sandwich.
On your cooked chicken, I place a slice of fresh mozzarella and either slide it under a broiler briefly (if indoors) or melt it on the grill. Once the cheese is melted, I spread about a generous tablespoon of pesto on the top half of each roll, place the chicken on the bottom half, add the sliced tomato and arugula, then crown it with the pesto-coated top bun. Serve immediately while warm and crisp.