In a large pot, bring water to a vigorous boil, then season generously with salt. Add penne pasta and cook according to package directions until al dente, about 8-10 minutes. Reserve ½ cup of pasta water before draining.

While the pasta is cooking, heat a deep skillet over medium-high heat and add olive oil. Add chopped red onion and carrots, sautéing for around 2 minutes until softened.

Add broccoli florets and diced bell pepper to the pan. Cook for an additional 2 minutes, stirring frequently.

Stir in zucchini and yellow squash, sauté for 2-3 minutes until tender.

Add minced garlic and chopped tomatoes, sprinkle in Italian seasoning, and cook for an additional 2 minutes.

Combine sautéed vegetable mixture with drained penne in a large bowl and toss gently.

Drizzle lemon juice over the pasta and gradually add reserved pasta water to achieve desired consistency.

Fold in grated Parmesan cheese and sprinkle with parsley before serving.