Pre-heat your oven to 180C, place the sweet potatoes on a baking tray and bake in the hot oven for 30 - 40 minutes or until soft. Set aside to cool.
Prepare the bulgur wheat by soaking it in lukewarm water for 20 minutes, then drain it in a sieve and let all excess water drip away.
Add a good glug of olive oil to the baking tin and arrange the sliced onion pieces in a single layer on the bottom.
Turn the oven up to 200C. Use a ricer to rice the potatoes until smooth. Combine them and the drained bulgur in a very large bowl with the grated onion, salt, cumin, cinnamon, chilli flakes, black pepper, garlic, coriander, and gram flour. Mix thoroughly to make sure everything is combined.
Add large spoonfuls of the mixture evenly over the sliced onions in the pan. Use a spatula to spread the mixture evenly over the entire baking tin.
Use the back of a knife to score diamond shapes (or any pattern you like) into it, going almost all the way through. Evenly pour the olive oil over the entire surface of the kibbeh and swirl it around to coat. Bake for around 50 minutes or until it is golden brown on top.
If after 50 minutes it hasn’t turned golden brown, turn on your grill and grill the kibbeh for 3 - 5 minutes until it starts to change colour - this just ensure the kibbeh won’t dry out.
Remove from oven and let sit for 5-10 minutes to cool slightly. You can re-score any cuts that may have sealed over. Use a spatula to remove pieces of the kibbeh, making sure you scrape up the onions on the bottom.