In large pot of boiling water, cook beets for about 45 minutes or until tender. Drain and let cool. Slip skins from beets. Cut into 1/4-inch (5 mm) thick slices; cut into 1/4-inch (5 mm) thick strips. Place in bowl.
In small bowl, whisk together cider, vinegar, oil, mustard, salt, pepper and sugar; stir in garlic and green onions. Add 2 Tbsp (25 mL) of the dressing to beets and toss to coat. Let stand for at least 30 minutes or for up to 8 hours.
Tear spinach into bite-size pieces; place in large bowl. Add apple and remaining dressing; toss to coat well. Arrange beets over top.