Using a fork, pierce each sweet potato several times. Place sweet potatoes directly on middle rack of oven. (Tip: Place a foil-lined sheet pan on the rack below the potatoes.)
Bake for 45-60 minutes, or until sweet potatoes can easily be pierced by a fork.
Remove sweet potatoes from oven and let cool until they are able to be handled.
Meanwhile, use paper towels to press as much liquid as possible from the thawed spinach.
Using a medium bowl, add remaining ingredients (drained spinach, cilantro, olive oil, lemon juice, garlic, oregano, salt, pepper, feta cheese and sun-dried tomatoes); stir until well combined.
Once sweet potatoes have cooled, slice each potato lengthwise.
Scoop out most of the sweet potato, leaving the potato skins intact. Add scooped out sweet potato to the bowl with the spinach; stir until well combined.
Stuff sweet potato halves with the spinach and feta mixture.
Place halved sweet potatoes on a foil-lined baking sheet and bake for 8-10 more minutes. Serve hot.