Preheat the oven. Heat the oven to 375°F.

Cook the spinach. Heat the olive oil in a large skillet over medium-high heat. Add the minced garlic and sauté for about 30 seconds, until fragrant.

Wilt the spinach. Add half of the spinach and half of the salt. Cook for about 3 minutes, until wilted. Add the remaining spinach and cook for another 3 minutes.

Drain the vegetables. Transfer the spinach to a colander and press gently to remove as much excess liquid as possible.

Cook the zucchini. Add the zucchini coins to the same skillet and cook for about 3 minutes. Transfer to the colander and drain off excess liquid.

Prepare the ricotta mixture. In a small bowl, combine the ricotta, egg yolks, nutmeg, and remaining salt. Stir until smooth.

Start layering. Spread 1 cup of marinara sauce across the bottom of a deep 9 × 13-inch baking dish. Arrange half of the polenta slices over the sauce.

Add the first layer of filling. Spread half of the spinach and zucchini mixture over the polenta, followed by half of the roasted red peppers.

Continue layering. Add half of the remaining marinara, half of the ricotta mixture, half of the mozzarella, and half of the Parmesan.

Repeat the layers. Use the remaining polenta, vegetables, roasted peppers, marinara, ricotta, mozzarella, and Parmesan to create a second layer.

Bake covered. Cover the baking dish with foil and bake for 30 minutes.

Finish uncovered. Remove the foil and bake for another 15–20 minutes, until heated through and the cheese is melted and bubbly.

Rest and serve. Remove from the oven and let the lasagna rest for 10 minutes before slicing and serving.