Adjust rack to top position and heat broiler to high. Wash and dry produce.

Pat salmon* dry with paper towels. Rub all over with oil; season with half the garlic powder, salt, and pepper. Place salmon, skin sides down, on a foil-lined baking sheet. Top with half the Parmesan, pressing to adhere.

Broil on top rack until salmon is cooked through and cheese is crispy, 4-8 minutes. (Check the fish frequently to make sure the crust isn’t burning!)

Meanwhile, zest and quarter lemon. Trim and discard root end from lettuce; chop leaves into bite-size pieces. Halve tomatoes. Halve, peel, and thinly slice half the onion (all for 4 servings); soak sliced onion in a small bowl with cold water.

In a large bowl, combine lemon zest, dressing, remaining garlic powder, juice from one lemon wedge (two wedges for 4 servings), salt, and pepper.

Add lettuce, tomatoes, sliced onion (draining first), and remaining Parmesan; toss until evenly coated.

Divide salad between shallow bowls. Top with croutons and salmon. Serve with any remaining lemon wedges on the side.