In a large bowl, combine chicken, salt and pepper, olive oil, garlic powder and Italian seasoning. Toss to combine.
Grill chicken over medium high heat for about 6-8 minutes on each side until cooked through. Top each piece of chicken with 1 oz of mozzarella cheese and cook another minute or so until melted.
Toss tomatoes, lemon juice and basil together. Top each chicken breast with 1 tablespoon of pesto, a scoop of tomato mixture and some freshly cracked black pepper (optional). Serve immediately.