Place 4 red-snapper fillets, skinned sides up, on a
work surface. Season with coarse salt; sprinkle with scallions and fresh thyme leaves. Divide 2 teaspoons unsalted butter among bottom halves of fillets; fold over top halves.
In a 12-inch skillet, combine corn and lima beans with fresh thyme; season with salt. Add water; bring to a simmer over medium heat. Place fish on top. Cover; steam until fish is opaque and vegetables are tender, 6 to 8 minutes. Garnish with more thyme.