(Can be done up to two days before as a side dish)
Pre-heat oven to 400 degrees. Poke holes in the sweet potato and microwave on high for one minute to soften potato, for easier peeling and chopping. Toss sweet potato cubes with olive oil and salt and pepper in a large bowl. Spread out onto baking pan. Roast the sweet potato cubes until soft, about 30-40 minutes. Set aside at least one serving or save leftovers.
(Can be done the day before, reserve dressing)
In a large bowl, toss spinach with balsamic dressing until leaves are thoroughly coated. Divide spinach between two plates or lunch containers. Top each with half of apples slices, half of roasted sweet potato cubes, and 2 tablespoons of feta per salad.