Preheat broiler. Generously butter a baking sheet. Arrange the trout fillets, skin side down, on the prepared sheet.
In a small bowl, combine the melted butter, salt, sage, and pepper. Using a pastry brush, coat each fillet with the seasoned butter, then sprinkle with breadcrumbs.
Broil the trout as close to the heat as possible, turning sheet as
needed for even cooking, until fish is golden brown and cooked through, 6 to 8 minutes. Serve with the lemon on the side.