• Preheat oven to 375°F (190°C). Line a baking sheet with parchment paper.

Prepare the filling

• In a medium skillet, heat 1 tbsp olive oil over medium heat. Add diced red onion and garlic (if using), sauté for 2-3 minutes until soft. Add bell peppers and cook another 3 minutes. Stir in spinach until wilted. Remove from heat and let cool slightly.

Mix filling

• In a bowl, combine sautéed veggies, lemon zest and juice, Parmesan cheese, panko, and egg whites. Season with salt and pepper.

Prepare sablefish

• Pat fillets dry and season with salt and pepper.

Assemble parcels

• Lay one sheet of filo dough on a clean surface. Brush lightly with olive oil or melted butter. Layer another sheet on top and brush again. Repeat until 3 sheets are stacked.
• Place one sablefish fillet near one edge of the filo stack. Spoon a generous amount of the veggie filling on top of the fillet. Carefully fold the filo over the fish and filling, wrapping it completely like a parcel. Seal edges with a little water or beaten egg white if needed.
• Repeat with remaining fillets and filo sheets.

Bake

• Place parcels seam side down on the prepared baking sheet. Brush tops lightly with olive oil or melted butter.
• Bake for 20-25 minutes, or until filo is crisp and golden and the fish flakes easily with a fork.
• Serve warm, garnished with lemon wedges.