Place 2 Tbsp. of the oil in a large skillet set over medium-high heat. Add the onion, bell peppers and garlic and cook until softened, about 3 to 4 minutes. Cool to room temperature; mix in the oregano, salt and pepper.
Preheat barbecue to medium-high. Layer the sheets of foil, slightly over-lapping them. Brush centre of the foil with remaining oil. Set the salmon in a row down the centre of the foil; season with salt and pepper. Top fish with onion/pepper mixture; drizzle with the lemon juice and wine. Fold the foil over the fish and seal the top. Set the salmon on one side of the barbecue. Turn the heat underneath it to low; leave the other side set to medium-high. Close the lid and cook the fish 20 minutes, or until cooked through.