Place the cleaned beets onto a large piece of foil. Tightly wrap the foil around the beets. Place on a baking sheet. Bake for 60-80 minutes until tender. (Start checking for doneness with a sharp knife around the 45-minute mark.)
Remove from the oven and carefully transfer the beets to an ice water bath. Remove the peels using your hands or a paring knife. Chop the beets into bite-sized pieces and place them into a large salad bowl.
In a medium mixing bowl, whisk together the olive oil, balsamic vinegar, and syrup until emulsified. Season with salt and pepper to taste.
To the bowl with the beets, add the spinach, arugula, half of the feta, nuts, and green onions. Pour the dressing over the salad and gently toss until coated.
Sprinkle the remaining cheese over the top and serve immediately.
Notes
A small casserole dish with a lid can be used instead of foil and a baking sheet if desired.
You can use precooked beets to save prep time. The beets can also be baked ahead of time and kept in an airtight container in the fridge for 2-3 days.
To toast the pecans: Place a skillet over medium heat. Add the nuts and toast for about 5 minutes until they are toasted, stirring occasionally. Transfer to a bowl to cool.