Bring 2 cups of vegetable broth to a vigorous boil. Gradually whisk in 1 cup of polenta, stirring continuously for about 5-7 minutes until thickened and creamy. Off the heat, gently mix in 1 cup of pumpkin puree, seasoning with salt and pepper.

In a skillet, heat 2 tablespoons of olive oil over medium heat. Sauté 1 diced onion for 3-4 minutes until softened, then add 2 minced garlic cloves, cooking briefly until fragrant. Fold in 2 cups of chopped fresh spinach and 1 teaspoon of Italian herbs, cooking until the spinach wilts. Season with salt and pepper to taste.

Preheat your oven to 375°F (190°C). In a greased baking dish, spread half of the polenta mixture as the base. Layer the spinach mix evenly on top, followed by half of the 1 cup of shredded mozzarella cheese. Cover with the remaining polenta, then sprinkle the rest of the mozzarella over the top.

Place the assembled casserole in the oven and bake for 25-30 minutes or until the top is golden brown and bubbly. Allow it to cool slightly before slicing.