14 ounces prepared polenta, sliced lengthwise into 6 thin slices
1 1/2 cups shredded vegan mozzarella (we like @FollowYourHeart brand)
Preheat oven to 450 degree F. Coat a 9-by-13-inch baking dish with olive oil or canola oil spray.
Heat oil in a large nonstick skillet over medium-high heat. Add Seitan (or Savory Grounds), eggplant, zucchini, squash, and bell pepper, salt and pepper and cook, stirring occasionally, until the vegetables are tender and just beginning to brown, 4 to 6 minutes. Add water and spinach; cover and cook until wilted, stirring once, about 3 minutes. Stir marinara sauce into the vegetables and heat through, 1 to 2 minutes. Remove from the heat and stir in basil.
Place polenta slices in a single layer in the prepared baking dish, trimming to fit if necessary. Sprinkle with 3/4 cup vegan cheese, top with the eggplant mixture and sprinkle with the remaining 3/4 cup vegan cheese. Bake until bubbling and the cheese has just melted, 12 to 15 minutes. Let stand for about 5 minutes before serving.