Heat oven to 400°F. Lightly spray small shallow baking dish with cooking spray.
Cut a pocket in each chicken breast by making a horizontal slit along thin long edge, being careful to not cut through to opposite side. Place sliced cheese in pockets. Brush chicken with melted butter; sprinkle with Italian seasoning, salt and pepper. Place in baking dish.
Bake uncovered 20 minutes or until juice of chicken is clear when center of thickest part is cut (at least 165°F).
On each of 2 plates, arrange tomato and cucumber slices. Drizzle with oil; sprinkle with salt and pepper. Place 1 chicken breast on each plate.