Bring a large pot of salted water to a boil. Cook penne pasta according to package directions, reserving 1/2 cup of the pasta water before draining.Meanwhile, heat olive oil in a large deep skillet over medium-high heat. Add red onion and carrot and sauté for 2 minutes.Add broccoli and red bell pepper, cooking for another 2 minutes.Stir in yellow squash and zucchini and sauté for 2–3 minutes, until veggies are just tender.Add garlic, grape tomatoes, and Italian seasoning. Sauté for 2 more minutes until fragrant and tomatoes begin to soften.Transfer cooked veggies to the pot with the pasta or a large bowl. Add drained pasta and drizzle with lemon juice.Toss everything together, gradually adding reserved pasta water until a light sauce forms.Mix in 1/4 cup of parmesan cheese and parsley. Serve hot, topped with the remaining parmesan.