In a large saucepan, heat the canola oil. Add the ginger, garlic, curry leaves, chopped chiles, turmeric, and 1 1/2 teaspoons of black pepper. Season with salt, and cook over moderate heat, stirring occasionally, about 8 minutes. Add the diced carrots, green beans, and vegetable stock, and bring to a boil; lower flame, and cook for 10 minutes. Add the fish cubes and the coconut milk and simmer, partially covered, until the vegetables are tender, fish is cooked, and the coconut milk is slightly reduced, about 10 minutes. Serve warm.