Marinate the Salmon
In a small bowl, mix grated ginger, lemon juice, soy sauce, and 1/4 cup maple syrup. Pour over salmon fillets in a shallow dish. Let marinate at room temperature for 15 minutes, turning halfway.
Preheat the Broiler
Place oven rack in the top position and preheat broiler.
Prepare the Glaze
Mix remaining 1/4 cup maple syrup with cayenne pepper.
Prepare for Broiling
Remove salmon from marinade and pat dry. Lightly season with salt. Place salmon fillets and pineapple slices on a rimmed baking sheet.
Glaze and Broil
Brush salmon and pineapple with glaze. Broil for 8–11 minutes, brushing again halfway through, until salmon is cooked through and lightly caramelized.
Serve
Top salmon with caramelized pineapple slices and serve immediately