Slice the eggplant into 1/4” slices and sprinkle liberally with salt. Place the slices in a colander to drain off any excess liquid. Let sit for 10 minutes, then rinse and pat dry with paper towels.
Place the eggplant slices and garlic head on a foil-lined baking sheet. Drizzle lightly with olive oil and sprinkle with salt and pepper. Roast for 45 minutes, or until the eggplant is tender, turning the tray once while cooking.
Remove the cooked eggplant from the oven and let cool. Peel away and discard the skin.
Preheat oven to 400 degrees F.
Squeeze the roasted garlic out of the remaining paper and into a food processor. Add in the roasted eggplant, tomato sauce, and most of the basil. Process until smooth, and then season with salt and pepper to taste. Add in half of the mozzarella and parmesan cheeses and process again.
Spray a baking dish with nonstick spray. Spread the roasted eggplant mixture in the dish and top with remaining mozzarella and parmesan.
Bake until browned, about 25 minutes. Serve warm with crostini, to dip.