Heat broiler. Cover broiling pan with aluminum foil. In large bowl, combine eggplant slices, olive oil, and salt. Place eggplant slices on broiling pan, and broil until tender, about 7 minutes. Let rest 10 minutes, or until cool enough to handle.
Heat oven to 375°F. Squeeze any excess liquid from spinach, and place in medium bowl. Add cheeses, garlic, and pepper. Stir to combine.
Place 2 tablespoons of spinach mixture onto center of each eggplant slice. Carefully roll up eggplant slices, and place end-side down in casserole pan. Brush with marinara sauce, and bake until cheese melts, about 12 minutes.