1. Rinse salmon and pat dry. Sprinkle all over with salt and pepper. In a small bowl, mix pecans, brown sugar, butter, lemon juice, and 1/4 teaspoon salt.
2. Place salmon on a 12- by 15-inch baking sheet. Broil 6 inches from heat for 6 minutes. With a wide spatula, turn fish over. Spoon pecan mixture evenly over fish and broil again, checking frequently to be sure nuts do not scorch, until fish is opaque but still moist- looking in the center of the thickest part (cut to test), 1 to 2 minutes longer.
3. With a wide spatula, transfer fish to serving plate.