Don't feel like fish? This bright salsa will also perk up chicken or pork.
Heat broiler, with rack in upper third. In a medium bowl, stir together avocados, pineapple, jalapeno, onion, cilantro, and lime juice. Season with salt.
Coat a rimmed baking sheet with cooking spray and place fish, skin side down, on sheet; season with salt and pepper. Broil until fish is opaque throughout, about 8 minutes. Top fish with salsa and serve with arugula.