Heat oil in a heavy saucepan over medium heat. Add the garlic and cook for 2 minutes, or until softened. Add the chili powder and cumin and cook over medium-low heat for 1 minute.
Stir in the stock, zucchini and rice, then cook over medium-high heat for 10 minutes or until the zucchini is just tender and the rice is cooked through (add enough additional time to ensure that the rice is tender). Season with salt and pepper.
Ladle into warm bowls garnish with oregano sprigs and serve immediately with lime wedges.