To prepare salsa: Cut the top and skin off pineapple, remove the eyes and core. Finely dice the pineapple (you will have about 4 cups diced pineapple) and place in a medium bowl. Add scallions, cilantro, lime juice, jalapeno and oil. Toss to mix. Season with 1/4 teaspoon salt and pepper. Serve immediately or cover and refrigerate for about 1 hour to allow flavors to blend.
To prepare fish: Combine flour, 1/2 teaspoon salt and 1/4 teaspoon pepper in a shallow dish; thoroughly dredge fillets (discard any leftover flour).
Heat oil in a large nonstick skillet over medium-high heat. Add the fish, working in batches if necessary, and cook until lightly browned and just opaque in the center, 3 to 4 minutes per side. Serve each portion of fish with about 1/4 cup salsa each.