For a vivid take on lunchtime tuna salad, use oil-rich sardines and skip the mayonnaise. Emulsifying the deeply seasoned oil from the sardine tin with lemon juice and mustard makes the salad creamy like mayonnaise does but with flavors that are more intense and pronounced. Add any of the sharp, crunchy, fresh pops you like in your tuna or whitefish salad, such as capers, cornichons, pickled peppers or herbs, and eat this sardine salad over greens, on a bagel or English muffin, or between two…