Preheat oven to 400 degrees F. Lightly coat a baking sheet with nonstick cooking spray. Peel eggplant, if desired; cut eggplant into 1/4-inch-thick slices.
Place marinara sauce in a shallow dish. In a second shallow dish combine crushed croutons and half the cheese. Dip eggplant in marinara and then in crouton mixture; press to coat. Place eggplant on prepared baking sheet. Lightly coat with cooking spray. Bake for 15 minutes or until breading is browned and eggplant is tender. Remove from oven.
On another baking sheet toast buns for 2 minutes or until lightly toasted. Meanwhile, transfer remaining marinara to a small microwave-safe bowl; heat in microwave for 30 seconds. Place eggplant on toasted bun bottoms; top with warm marinara, remaining cheese, and bun tops. If desired, sprinkle with basil leaves.