Preheat the oven to 350℉.
In a large bowl, whisk the cottage cheese, sour cream, mozzarella cheese, egg, and parsley (or dried Italian seasoning). Set aside.
Prepare penne according to package directions, until al dente. Then drain and set aside.
Meanwhile, heat the olive oil in a frying pan and sauté the zucchini, yellow squash, onions, and mushrooms over medium-high heat for about 5 minutes, until tender.
Reduce heat to low. Add marinara sauce and garlic powder. Stir while simmering over low heat, until heated through, about 1 to 2 minutes. Add salt and pepper to taste.
Spread 2 tablespoons of marinara sauce into the bottom of a 2-quart baking dish.
Place half of the penne in the baking dish.
Spoon half of the marinara sauce over the penne.
Dollop half the cheese mixture over the sauce.
Repeat the process, ending with dollops of the cheese mixture.
Cover with foil and bake for 25 minutes. Remove foil and continue cooking for an additional 5 minutes.
Allow to cool for 5 minutes before serving.