Cut the eggplant into very thin slices, about ⅛-inch thick.

Lay them on paper towels and sprinkle the eggplant slices with the salt. Let them rest for about 30 minutes.

Blot the eggplant slices with paper towels to remove any excess liquid.

In a bowl, mix the ricotta, spinach, garlic powder, and oregano. In another bowl, mix the mozzarella and Parmesan cheese.

Spray a slow cooker with nonstick cooking spray. Spoon ⅓ cup of the marinara sauce on the bottom of the slow cooker.

Arrange the about ⅓ of the eggplant slices over the marinara sauce, overlapping them and breaking them into large pieces to cover as much of the sauce as possible. Drizzle the eggplant with 1 tablespoon of the olive oil and add a pinch of black pepper.

Spread half of the ricotta mixture over the top of the eggplant. Drizzle with ⅓ cup marinara sauce and repeat with a layer of eggplant, 1 tablespoon of oil, a pinch of black pepper, one layer of ricotta mixture, and the remaining marinara sauce.

Add another layer of eggplant, and finish with a layer of mozzarella and Parmesan cheese. Sprinkle with the paprika, if using. Cover and cook on LOW for 4 to 5 hours or on HIGH for 2 to 3 hours, or until the eggplant is very tender.

Let it rest for about 5 minutes before serving. Garnish with fresh basil, if desired.