Preheat oven to 400.
Peel and cut sweet potatoes into 1/2” cubes.
Place cubed sweet potato on baking tray and coat with 1/2 to 1 tablespoon olive oil.
Season with salt and pepper.
Bake for 15-20 minutes or until fork tender.
While baking, heat a 1/2 tablespoon of olive oil in small saucepan.
Add diced onion; saute for 5 minutes.
Add cider and cranberries, and simmer for 5 minutes.
Add cider vinegar, and simmer for another 5 minutes.
When sweet potatoes are fork tender, remove pan from oven.
Immediately transfer sweet potatoes to a mixing bowl.
Top with baby spinach.
Pour hot cider mixture over potatoes and spinach.
Toss to combine.
Serve, topped with walnuts and/or blue cheese, if desired.