Preheat an oven to 350°F.

In a roasting pan, combine the beets, salt and pepper. Cover with aluminum foil and bake until tender, about 1 hour. When the beets are cool enough to handle, slip off the skins, then cut the beets into wedges.

In a bowl, whisk together the vinegar and mustard. Add the olive oil in a slow, steady stream, whisking constantly until blended.

In another bowl, combine the beets, half of the vinaigrette, salt, pepper, green onions and half of the mint. Toss to coat and let stand for about 30 minutes.

In a large salad bowl, combine the spinach, the remaining vinaigrette, the beet mixture, the oranges and the remaining mint and toss to mix. Divide the salad among 4 individual bowls, garnish with the raspberries and serve immediately.