In a medium saucepan, heat 2 Tbs of olive oil. Add the sliced onion, chopped scallions, sliced garlic, branches of thyme and strip of mandarina peel. Cook, stirring occasionally until the onion is soft, about 5 minutes. Stir in the mandarina juice and the white wine and simmer for 5 minutes. Let cool to room temperature.
Place the two filets of salmon on a parchment paper lined baking sheet. Drizzle them with olive oil and season with salt and freshly ground pepper. Slice the mandarinas into 1/4 inch thick slices and scatter them over one fillet. Spoon the onion and garlic mixture over the mandarina slices. Top with the other fillet, meat side down.
Roast in the oven for 30 minutes, or until almost cooked through (don’t overcook!)
Scoop out the onion and garlic filling. To serve, arrange the fish with the slices of orange on a platter and serve with the onion and garlic stuffing.