Preheat the oven to 375°F. Place the chicken breasts on a cutting board and cover tightly with plastic wrap. Using a rolling pin or meat mallet, gently pound the chicken until the pieces are thin and uniform in thickness. Spread the spinach evenly across the bottom of a large baking dish and drizzle with 1 tablespoon of olive oil. Arrange the pounded chicken breasts on top of the spinach. Drizzle the chicken with 2 tablespoons of olive oil, sprinkle with 1 teaspoon garlic powder, 1 teaspoon dried oregano, and season with salt and pepper to taste. Spread half of the diced tomatoes over the chicken, then evenly sprinkle all of the shredded cheese on top. Take a large piece of foil, oil one side, and cover the baking dish tightly with the oiled side facing down to prevent the cheese from sticking to the foil. Bake for 10 minutes. After 10 minutes, remove the foil and return the dish to the oven for an additional 10 to 12 minutes, or until the cheese is golden brown and the chicken is cooked through. (Cooking time may vary depending on the thickness of the chicken breasts.) While the chicken is baking, combine the remaining diced tomatoes with 2 tablespoons olive oil, 1 teaspoon garlic powder, 1 teaspoon dried oregano, lemon juice, and chopped basil in a small bowl. Season with salt and pepper as needed. Once the chicken is done, remove it from the oven and let it rest briefly before serving. Top each portion with the tomato mixture and enjoy.