Heat oil in large skillet over medium-high heat; add mushrooms, peppers, onions and spinach, and cook 5 minutes, or until water evaporates.
Mix cottage cheese, 2 cups mozzarella cheese and salt in mixing bowl.
Assemble lasagna in slow cooker as follows: ⅓ of pasta sauce, single layer noodles, ⅓ of cooked vegetables, single layer zucchini and ⅓ of cottage cheese mixture. Repeat for another 2 layers. Sprinkle ½ cup mozzarella cheese on top.
Cook on low 5 hours, or until noodles and zucchini are tender.