You will need

8 ounces baby spinach, about 5 to 6 cups
1 cup mandarin oranges, drained tnned or use fresh
1/2 cup chopped red onions
1 tablespoon orange marmalade
2 tablespoons red wine vinegar
1/3 cup extra-virgin olive oil.
Salt and pepper 

This is how you do it

Arrange spinach leaves on a large platter or individual salad plates. Top with mandarin sections and chopped red onion. Whisk together marmalade and vinegar. Stream oil into dressing while continuing to whisk.