Heat 2 tablespoons olive oil in a large nonstick skillet over medium heat.
Sauté the diced onion for about 2 minutes, until slightly softened.
Add the diced zucchini, grated carrot, and diced green pepper; sauté another 5–7 minutes until vegetables are tender.
Stir in the minced garlic and cook about 1 minute until fragrant.
Mix the tomato paste into the sautéed vegetables until well combined.
Add the diced tomatoes (14.5 oz can), 1 can tomato paste (if separate), 2 cups V8 juice, dried basil, dried oregano, bay leaf, and 1 1/2 tablespoons sugar; stir to combine.
Bring the sauce to a boil, then reduce heat to a simmer.
Cover and simmer for about 30 minutes, stirring occasionally; add a little water if you prefer a thinner sauce.
Season with salt and pepper to taste, remove and discard the bay leaf, and serve over hot spaghetti with parmesan if desired.