Place bed of greens on four plates. Cut off ends of oranges and grapefruit, revealing the flesh. Slice each orange on a cutting surface, and with sharp knife, slice off peel, making sure to remove all the peel and white membrane. Repeat same procedure with grapefruit. Slice oranges and grapefruit, removing all seeds. Lay slices of orange and grapefruit on greens. Lay concentric rings of red onions over fruit. Sprinkle with mint. Drizzle Salads with Lingonberry (Partridgeberry) Vinaigrette. Serves 4. Combine all vinaigrette ingredients and whiisk together until blended.