1 tablespoon onion and spice seasoning blend (such as Mrs. Dash® Original Seasoning)
or to taste
Preheat an outdoor grill for medium-high heat and lightly oil the grate.
Rinse salmon thoroughly and place on a layer of aluminum foil. Pour lemon juice on top. Sprinkle onion and spice seasoning over fillets. Add lemon slices and onion.
Place a second sheet of aluminum foil over salmon and tightly secure to ensure moist fish. Place packet on the upper rack of the grill and cook, 15 to 20 minutes. Flip, being careful not to tear the aluminum foil. Continue grilling, about 15 to 20 minutes. If salmon is completely sealed, cook until fish flakes easily with a fork, about 10 minutes more.
Place salmon on a platter. Peel off skin with a spatula.