Filling: Cook onions on medium heat until translucent. Add garlic. Cook about 30 seconds. Add spinach and salt. Cook until wilted. Mix with tofu ricotta in a food processor.
Preheat oven to 350°.
Roll Ups: Slice zucchini 1/16" thick on a mandoline. Lay sliced zucchini on a cutting board that is covered with a kitchen towel or paper towels. Sprinkle each slice with salt. Let sit for 15 minutes or until the zucchini starts to sweat, where water is drawn to the surface. Pat each zucchini slice off.
Spread about ½ cup marinara sauce on a baking dish (mine was 7 ½" x 9 ½").
Spread about a teaspoon of filling on each piece of zucchini. Roll tightly. Place on top of marinara sauce in baking dish. Repeat with the rest of zucchini. If you have extra filling, spread on top of zucchini rolls. Pour the rest of marinara sauce on top.
Bake at 350° for 30 minutes, or until zucchini is crisp tender.