Preheat the oven to 400 F/ 200 C/ gas mark 6. Line a baking tray with parchment paper. Cut the sweet potatoes in half lengthways and place on the tray cut side up. Drizzle with a little oil using a basting brush to spread it evenly and bake for 30-35 minutes or until tender.
Remove the potatoes from the oven and using a small spoon or melon baller scoop out the middle (not too much, about 1.5-2 tsp from each half). Combine with the spinach, garlic, feta and 1 tablespoon of the oil, add pepper to taste and blitz the mixture is sticky. Do not overblend.
Divide the mixture between the potato halves, drizzle with a little oil and bake for an additional 10 minutes. Serve hot or cold.
I used small sweet potatoes in this recipe mainly because they don't take long to cook and work better as an appetizer. But you can use large ones too, just increase baking time as well as the amount of spinach and feta. Once you've blitzed the mixture taste it to check if you like it and add more spinach or feta to suit your preference.
Try not to process the filling too much and turn it into a puree.
Serve hot or cold.
Freeze in a single layer in an airtight container for up to 3 months.