Preheat oven to 400 degrees. Slice half the polenta into 1/2-inch thick rounds. Place them on an oiled baking sheet and season with salt and pepper. Bake for 30 minutes, until crispy.

Meanwhile, thinly slice the zucchini. Thinly slice the garlic. Halve, peel, and finely chop the onion. Coarsely chop the olives.

Toss the zucchini with 1/2 tablespoon olive oil and a pinch of salt and pepper. Spread them out on another baking sheet and roast for 10 minutes until softened.

While the zucchini roasts, heat 1/2 tablespoon olive oil in a pan over medium heat. Add the onion and season with salt and pepper. Cook for about 5 minutes, until softened.

Add the crushed tomatoes and oregano to the pan with the onions. Simmer for about 5 minutes, until sauce has slightly thickened. Season with salt and pepper.

In another pan, heat 1/2 tablespoon olive oil. Add the garlic and spinach and season with salt and pepper. Cook, tossing, for about 2 minutes until wilted.

Serve the sautéed spinach with polenta cakes and roasted zucchini on top. Spoon over some tomato sauce and sprinkle with goat cheese, walnuts, and olives.