Heat oven to 450º F. Lightly coat 2 baking pans with cooking spray. In a bowl, toss the sweet potato slices with oil.
Arrange potatoes in a single layer on one baking pan. Sprinkle with half the rosemary. Place in the oven and roast until tender, about 30 minutes.
Meanwhile, season each side of the meat or salmon with salt and a few grinds of pepper. Spread with mustard. Sprinkle with sugar and remaining rosemary.
Arrange the meat or fish on the second baking pan. Roast, turning once, until cooked through, 20 minutes for pork or chicken, 10 minutes for salmon.
Check the potatoes for tenderness; cook longer if necessary. Arrange on 4 plates and top with the meat or fish. Cover to keep warm.
Place the baking pan used for the meat or fish over medium heat on the stovetop. Add the orange juice and cook until slightly thickened, about 2 minutes. Pour the juice over meat or fish. Season with salt and pepper to taste.