In a medium mixing bowl, toss the zucchini ribbons with the salt until evenly mixed. Set aside.

Heat the olive oil in a large (12-inch) skillet over medium heat. Add the mushrooms, onion, and salt, and sauté until the mushrooms have given up their liquid and the onions are beginning to brown, about 15 minutes. Set aside and allow to cool.

When the mushroom mixture has cooled, transfer it to a large mixing bowl. Add the rest of the meatball ingredients and stir to combine evenly.

Preheat the oven to 400ºF and line a baking sheet with parchment paper or aluminum foil.

Use a medium cookie scoop to portion the meatball mixture into even balls and place them on the cookie sheet. Bake for 30 minutes, until cooked through and beginning to brown.

Pour the marinara sauce into a medium (3 1/2-quart) heavy-bottomed pot or dutch oven, and place over medium heat.

Add the cooked meatballs to the sauce, bring up to a simmer, and turn down to low. Let simmer for 30 minutes.

While the meatballs are simmering in the sauce, put the salted zucchini into a colander or large strainer, and rinse it well with fresh water. Allow to drain thoroughly.

Place the zucchini “noodles” in individual bowls, and ladle the hot meatballs and sauce over the top of each portion.