Preheat the oven to 450°F (232°C). Line a rimmed baking sheet with aluminum foil or parchment paper to prevent sticking and make cleanup easier.

In a small skillet or saucepan, melt the butter over medium heat. Add the minced shallot and sauté for approximately 3 minutes, or until softened. Stir in the minced garlic and lemon zest, cooking for an additional minute until fragrant. Remove from heat and allow the mixture to cool slightly. Stir in half the lemon juice.

Place the steelhead trout fillet on the prepared baking sheet. If the fillet is too large, position it diagonally. Season the fish generously with salt and ground black pepper.

Spoon the prepared butter sauce evenly over the fish, ensuring it is well coated. Sprinkle half of the minced dill over the top of the fillet.

Transfer the baking sheet to the preheated oven and roast the trout for 12–17 minutes. The exact cooking time will depend on the thickness of the fillet. To check for doneness, gently insert a fork into the fish; it should flake easily.

Carefully transfer the cooked trout to a serving platter, using multiple spatulas if necessary to maintain its shape. Squeeze the remaining lemon juice over the fish and garnish with the remaining fresh dill. Serve immediately.