Preheat your oven to 350°F / 175°C.
While the oven heats, prepare the dukka.
Spread the almonds on a baking sheet and toast for 5-7 minutes, until light brown and fragrant.
Transfer to a bowl to cool.
Meanwhile, add the coriander seeds, cumin seeds, and salt to a dry skillet over medium-low heat. Toast for about 3 minutes, swirling the pan constantly, until fragrant.
Add to the bowl with the toasted almonds and let everything cool completely.
Once cooled, place the almond-spice mixture and sumac into a food processor or mortar and pestle. Coarsely grind the mixture.
Transfer to a bowl and stir in the toasted sesame seeds.
Set aside.
Poke the sweet potatoes all over with a fork.
Place them on a baking sheet and bake for 1 hour, or until very soft when pierced with a knife.
Let them cool for about 10 minutes, until you can handle them.
Slice each sweet potato in half lengthwise. Carefully scoop the flesh into a large bowl, leaving a thin border to keep the skins intact.
Add the olive oil to the sweet potato flesh and mash until smooth. Gently fold in the crumbled feta cheese, trying not to break it up too much.
Arrange 8 of the best-looking potato skins on the baking sheet. Spoon the mashed sweet potato filling evenly into the skins.
Sprinkle each generously with about 1 Tbs of the prepared dukka.
Bake for 10-15 minutes, or until the filling is piping hot.
Serve immediately.
