In a large wok or skillet, heat the coconut oil over medium-high heat. Add the eggplant and sauté, stirring occasionally, until lightly browned, about 5 minutes. Add the zucchini with a pinch of salt. Cook, stirring, 3 minutes. Stir in the ginger, tomatoes and potatoes (if using); season with salt. Cook 2 minutes, or until fragrant. Add the coconut milk mixture and bring to a simmer. Cook until the vegetables are tender, about 5 minutes. Remove the pan from the heat; stir in the herbs and 1-2 tablespoons lime juice, to taste. Season with salt.