Prepare your vegetables: dice zucchini, chop onion, mince garlic, and dice bell pepper.
In a large skillet over medium heat, warm olive oil. Add onion and sauté until softened (5–7 minutes). Then add garlic and bell pepper; cook until fragrant (2–3 minutes).
Stir in uncooked rice to coat with oil; toast for about 1 minute while stirring.
Add undrained diced tomatoes and vegetable broth along with oregano, basil, red pepper flakes (if using), salt, and pepper.
Bring to a boil then reduce heat to low. Cover and simmer for 20–25 minutes until rice is tender and liquid is absorbed.
Gently stir in diced zucchini; cover again and simmer for another 5–7 minutes until zucchini is tender-crisp.
Remove from heat; stir in grated Parmesan cheese until melted.
Let rest for 5 minutes before serving and garnish with fresh parsley.