Preheat the oven to 400 degrees F (200 degrees C). Line a baking sheet with aluminum foil.

Toss bread crumbs with onion, dill, lemon zest, garlic, and 1/2 of the olive oil. Season with salt and pepper to taste. Press stuffing into trout, then brush with remaining olive oil; season with salt and pepper. Place trout onto the prepared baking sheet.

Roast in the preheated oven until skin begins to brown, and the flesh flakes easily with a fork, about 20 minutes.