1. Sprinkle eggplant on both sides with salt, place on paper towels, and let stand for 20 minutes. Rinse; blot dry.
2. Mist inside of slow cooker with cooking spray. Spread 1/4 cup marinara over bottom. Dip eggplant in egg, then coat with bread crumbs. Arrange a layer of eggplant over sauce. Top with 1/4 cup sauce; sprinkle with 1/2 cup mozzarella. Layer sauce, eggplant and cheese, ending with cheese (about 4 layers), filling cooker 2/3 full.
3. Cover and cook on low until eggplant is soft and cheese has melted, 4 to 6 hours. Spoon onto plates, sprinkle with basil and serve.