For the tartar sauce:
1 cup Greek yogurt, whole milk or reduced-fat
½ lemon, juiced (about 2 tablespoons)
¼ cup fresh dill sprigs, finely chopped
3 tablespoons finely chopped onion or shallot
3 tablespoons sweet pickle relish
2 tablespoons Dijon mustard
2 tablespoons small capers
1 clove garlic, grated or pasted
Salt and pepper
For the fishwiches:
4 tilapia fillets, or other thin mild white fish fillets (6 to 8 ounces each)
1 teaspoon granulated garlic
Salt and pepper
½ lemon, plus 1 lemon, cut into wedges, for serving
About ½ cup flour, for dredging
About 3 tablespoons cornstarch
3 large eggs
About 3 tablespoons milk, half-and-half, or heavy cream
1 tablespoon vegetable or safflower oil
3 tablespoons butter
8 slices good-quality white bread, lightly toasted
Shredded iceberg lettuce, for topping
Preheat the oven to 200°F. For the sauce, in a medium bowl, stir the yogurt, lemon juice, dill, onion, pickle relish, Dijon, capers, and garlic; season with salt and pepper.
For the fish, sprinkle the fillets with the granulated garlic; season with salt and pepper. Squeeze the juice from the ½ lemon on top of the fish. In a shallow bowl, whisk the flour and cornstarch. In a second shallow bowl, whisk the eggs and milk; season with salt.
In a large nonstick skillet, heat the oil, one turn of the pan, over medium-high. Add half the butter. Dredge 2 fillets in the flour; coat with the egg. When the butter stops foaming, add the fish. Cook, turning occasionally, until opaque in the centers, 6 to 7 minutes. Transfer to a baking sheet and keep warm in the oven. Repeat with the remaining butter, fish, flour, and eggs.
Serve with lemon wedges. Top the toast with some shredded lettuce and the fish — and lots of tartar sauce.