Meanwhile, in a large saucepan, heat the vegetable oil. Add the garlic, leek and ginger and cook over moderately low heat, stirring occasionally, until softened, about 5 minutes. Add the curry powder and cook, stirring, until fragrant, about 3 minutes. Add the tomatoes and cook, stirring, for 2 minutes. Add the remaining 1 1/2 cups of water, the soy sauce and the potatoes. Cover and simmer until the potatoes are tender, about 10 minutes. Add the okra and simmer until just tender, about 3 minutes. Add the snow peas and spinach and simmer until the snow peas are bright green, about 1 minute. Stir in the lentils, add the lime juice and season with salt and pepper. Serve hot or warm.