In a large saucepan, heat the olive oil over medium heat. Add the onion and saute until soft and translucent, about 4 minutes. Add the garlic and saute for 30 seconds; don't let the garlic brown. Add the tomatoes, oregano and cumin and saute until the tomatoes are softened, about 4 minutes.
Add the stock and bay leaf and bring to a boil, then reduce the heat to medium low and bring to a simmer. Add the carrot and bell pepper and cook for 2 minutes. Add the zucchini and simmer until the vegetables are tender, about 3 minutes longer. Stir in the lemon zest and cilantro. Season with the salt and pepper. Discard the bay leaf.
Ladle into individual bowls or mugs and serve immediately.