Heat the olive oil in a large pot over medium heat.
Add the diced onion and cook for 3-4 minutes until softened.
Add the minced garlic and cook for 1 minute until fragrant.
Add the diced zucchini, red bell pepper, and cherry tomatoes to the pot and cook for 3 minutes, stirring occasionally.
Add the dried penne pasta, vegetable broth, diced tomatoes with juice, dried oregano, dried basil, salt, black pepper, and red pepper flakes to the pot. Stir to combine.
Bring the mixture to a boil, then reduce heat to medium-low and simmer uncovered for 12-15 minutes, stirring occasionally, until the pasta is cooked and most of the liquid is absorbed.
Remove the pot from heat and stir in the grated Parmesan cheese and chopped fresh parsley.
Serve immediately, garnished with additional Parmesan and parsley if desired.