Oil a 9 x 13-inch or 8 x 12-inch casserole dish.

Using a spiralizer, make zucchini noodles (zoodles) following the manufacturer's directions. You should have a generous 8 cups of zucchini noodles. Place in a colander over a bowl. Snip the zucchini noodles with scissors here and there to keep them from tangling too much. Toss the zoodles with 1 ½ teaspoons of salt. Let the zoodles drain of excess moisture while you make the sauce.

Coat the bottom of a large sauté pan with olive oil. Break up the Italian sausage into small clumps in the pan. Heat on medium heat and gently cook the sausage until it is just cooked through and lightly browned. Remove to a bowl. Discard all but 1 tablespoon of rendered fat.

In the same pan, add the chopped onion. Cook until softened and lightly colored, about 5 to 6 minutes. Add the minced garlic and cook 1 minute more.

Add the canned crushed tomatoes and cooked sausage to the pot with the onions. Bring to a simmer and lower the heat to maintain a low simmer. Cook for 5 to 6 additional minutes. Stir in the thinly sliced basil and ½ teaspoon of kosher salt.

Add the zucchini noodles to the pot with the tomato sausage sauce. Gently stir to combine so that all of the noodles are coated with sauce. Transfer to the prepared casserole dish and spread into an even layer.

Arrange the ricotta in clumps on the casserole. Press the ricotta into the zucchini noodles to penetrate the casserole a bit. Mix the grated mozzarella and Parmesan cheese together and sprinkle over the top in an even layer.

Bake at 350°F, uncovered, for 35 minutes, or until the top is lightly browned and bubbly. Let cool for 10 minutes before serving.