In a heavy skillet, heat the oil over medium heat until shimmering. Add the onion and cook, stirring occasionally, until golden brown, about 5 minutes. Add the garlic and ginger and cook until softened, about 2 minutes. Add the jalapeño, tomatoes, coriander and turmeric and cook until the tomatoes are soft, about 3 minutes. Add the okra and ½ cup of water. Cover the skillet and cook, stirring occasionally, until the okra is tender, about 15 minutes. (If the pan becomes too dry, add more water.) Season with salt and pepper and serve.