How to Make It
In a dry skillet, toast the mustard seeds over moderate heat until they darken and begin to pop, about 2 minutes. Transfer to a plate. In a bowl, whisk the mayonnaise with the mustard, dill, lime juice and brown sugar. Season with pepper.
Light a gas grill. Lightly brush the grate with oil. Run your fingers over the salmon fillet, feeling for bones; use sturdy tweezers to remove any you find.
Brush the skin side of the salmon with the olive oil and season generously with salt and pepper. Set the fillet on the grill, skin side down, and spread the mustard glaze over the fish. Sprinkle with the toasted mustard seeds. Close the grill and cook over moderate heat until the glaze is golden and the fish is nearly opaque, about 25 minutes. If the skin begins to char, reduce the heat to low and move the fish to a cooler part of the grill. Transfer the salmon to a platter and serve hot or at room temperature.