I used mustard to spice up these lentils. While mustard is used often enough in Indian cooking, I used it a little differently here than I usually do: I ground it up before adding it. Mustard adds a spicy, almost slightly sour punch to the curry, and I couldn’t have been happier.The addition of spinach makes this curry even healthier. Feel free to substitute other greens, including watercress. Check to get new recipe updates by email.