Preheat oven to 400°F/205. Use a fork to poke holes around the sweet potatoes to allow steam to escape as they cook.
Once fully heated, place the sweet potatoes in the oven on a large baking sheet. Let cook about 45 minutes to an hour (depends on how big the sweet potatoes are) or until tender to the touch.
While the potatoes cook prep your filling: Warm the olive oil in a large skillet. Add the garlic and cook for a 1-2 minutes on a medium-low until golden and fragrant, stirring the whole time to keep from burning.
Add the spinach and lemon juice to the pan. Cook uncovered, about 2-3 minutes until the spinach is wilted.
Stir in the sun dried tomatoes, feta and stir. Cook a few minutes to heat through then set aside away from the heat until the sweet potato finish cooking.
After removing the potatoes from the oven slice an opening down the lengthwise. Spoon the filling into the potatoes, top with more feta if desired and serve.