Roasted Beets and Citrus with Feta

Name: Roasted Beets and Citrus with Feta
Ingredients: 3 tablespoons balsamic vinegar; 2 teaspoons Dijon mustard; 2 teaspoons finely grated orange peel; 2 teaspoons finely grated grapefruit peel; 1 teaspoon honey; 1/3 cup extra-virgin olive oil; 4 2 1/2-inch-diameter unpeeled beets, tops trimmed; 1 tablespoon olive oil; 1 6-ounce bag baby spinach; 2 small pink or ruby grapefruits, all peel and pith cut away, segments cut from between membranes; 2 oranges, all peel and pith cut away, segments cut from between membranes; 3/4 cup crumbled feta cheese (4 ounces); 1/4 cup chopped fresh chives