Preheat the oven to 375 degrees F. Place the first 6 ingredients in a large bowl, whisk to combine, and then set aside.
Place the salmon in a parchment paper lined baking pan. Drizzle with the olive oil orange juice mixture and season with salt and pepper. Roast for 15 minutes, or until cooked through.
When the salmon is cooked, add the salad greens, oranges, onion and tomatoes to the dressing in the bowl and toss to combine. Divide the salad among 6 plates, ensuring some of orange, onion and tomato decorate the top. Set a piece of salmon on each plate and serve.