Preheat oven to 375 degrees F.Toss onion, garlic, and zucchini with oil and lay flat on a sheet pan. Roast for 25 - 35 minutes, until zucchini is tender and browned, tossing occasionally.Add onion, garlic, and zucchini to a blender with basil, oregano, and stock and blend until smooth. Add sea salt and black pepper to taste.Top with the diced red onion, tomato, and drizzle of olive oil, if using. Add extra black pepper if desired. Serve warm or cold.