Using a mandoline, slice the zucchini lengthwise. Place the zucchini on a flat surface and sprinkle with salt. Let it sit for at least 20 minutes. Set aside.

Wash and trim the stems from the spinach leaves. Chop the onion and sauté in a pan with butter and garlic for three minutes. Add the chicken and cook a little longer until almost done, then add the chopped spinach and mix well.

Now add the mascarpone and Parmesan cheeses to the spinach and mix well. Cook for one minute and turn off the heat.

To make the ravioli: Before using, rinse and dry the zucchini well with a paper towel to remove excess moisture. To form them: place 2 strips of zucchini in a cross and 2 in an X, forming an asterisk with them, and place a tablespoon of filling in the middle. Close the package and secure with a toothpick.

Once all the ravioli are formed (the number depends on the size of the zucchinis and the thickness of the slices), cover the bottom of a baking dish with tomato sauce. Place the ravioli on top, drizzle a little oil over them, and sprinkle with mozzarella cheese.

Bake at 250°F for 15-20 minutes (preferably with the oven fan on to evaporate all the vegetable liquid), until the sauce has reduced and the zucchini is cooked and toasted on top. Remove from the dish and serve immediately; you can also add a little pesto sauce.