Place the eggplant cubes in a large bowl, add one tablespoon of salt, cover with water and let it soak for 2 hours. Drain eggplant cubes and pat dry with paper towels.
Preheat the oven to 400F (205C).
Spread the walnuts on a parchment-lined baking sheet and toast them in the oven for 4 minutes or until fragrant.
Place the cubes back in the large bowl, add ¼ cup olive oil and toss it to coat. Spread the cubes in one layer in a large baking pan—Bake for 30 minutes. Remove from the oven and let it cool for 15 minutes.
Add onion, garlic, walnuts, parsley, nutmeg, salt, black pepper, and the roasted eggplant to a food processor bowl and pulse until well combined into a smooth texture. Scrap the eggplant mixture into a large bowl, add panko, and stir until combined using a spatula.
Preheat the oven to 375F (190C).
Line a large baking pan with parchment paper. Using an ice cream scoop or a ¼ cup portion, scoop the eggplant mix, and roll them into balls with your hands. Place the eggplant balls onto a parchment-lined baking sheet. Gently brush them with olive oil and bake them for 18 minutes or slightly brown.
Add the marinara sauce to a large pot over high heat and heat it for 3 or 4 minutes; add the meatless eggplant balls and serve hot.