From orange, grate 1/2 teaspoon peel and squeeze 3 tablespoons juice.
In saucepan, heat oil and grated orange peel on medium-high until hot. Add spinach, in 2 to 3 batches, cooking and stirring about 3 minutes or until spinach begins to wilt and it all fits in saucepan. Cover and cook 2 minutes longer, stirring once. Remove saucepan from heat; stir in orange juice and salt. Garnish with orange peel.