In a large pot add water and bring to boil. Add the beetroots and boil until fork tender.
After boiling beetroots, add in the pot cold water and leave the beetroots on it in order to cool. It will take about 30 minutes. Then rub off the skin from the beets and chop them.
Whisk vinegar, mustard, and honey in small bowl. Gradually whisk in oil. Season vinaigrette with salt and freshly ground black pepper.
Place spinach and onion in large bowl; toss with vinaigrette.
Add beets segments, orange segments and sprinkle with cheese and walnuts.