Preparation

• Put half of the salmon in a food processor and pulse until it’s coarsely chopped. Transfer to a medium bowl. Chop the remaining salmon in the same manner, and add to the bowl. Fold in the shallot, capers, mustard, and 3/4 tsp. each salt and pepper. Form into four 3/4-inch-thick patties, set on a large oiled plate and cover, and refrigerate until ready to cook (up to 4 hours).
• Meanwhile, make the tartar sauce. In a small bowl, mix the mayonnaise with the relish, dill, lemon juice, and 1/4 tsp. each salt and pepper. Taste and add more lemon juice, salt, and pepper if needed. The sauce will keep for up to one day in the refrigerator.
• Heat the oil in a large (12-inch), nonstick skillet over medium-high heat until it’s shimmering. Add the salmon burgers (straight from the refrigerator; the cold temperature will help them hold together), reduce the heat to medium, and cook without touching until they brown at the edges, 2 to 3 minutes. Flip and cook the other sides until they, too, are browned and the burgers are just a little pink in the center (check by slicing into a thicker part of one of the burgers with a paring knife), about 3 to 4 more minutes.
• Put the spinach, onion, and 2 tomato slices on each of the buns; top with the burgers and a dollop of the tartar sauce; add the top of the bun and serve.

Try ourGrillied Zucchini with Chive Oilas a side dish.