In a blender, puree pineapple, ginger, garlic, soy sauce, and brown sugar. Pour into a baking dish and place salmon, skin side up, on top of marinade. Cover dish with plastic wrap and place in refrigerator for 30-60 minutes.
Place oven rack close to broiler. Preheat a dry (no oil) cast iron skillet or other heavy bottomed skillet over high heat on the stovetop until very hot. Place salmon in pan, skin side down, then immediately transfer to broiler for about 2 minutes, or until salmon is translucent and just cooked through. Cooked salmon should flake easily with a fork.
Top with Pineapple Habanero Salsa and scallions. Serve immediately.