In a large bowl add the flour, sugar, salt, baking powder, garlic, nigella seeds, salt & 1 tablespoon finely chopped coriander.
Make a well then add the milk and oil. Slowly mix together the dough by working from the centre and incorporating the flour from the edges to make a smooth, soft dough. Knead for 8-10 minutes. Place the dough into an oiled bowl, cover with a damp tea-towel and leave in a warm place for 10-15 minutes.
Form the dough into 2 balls. And roll them out to a large circle. Brush with melted butter then cook in a large frying pan for a couple of minutes on both sides.
Top each flatbread with some leftover chicken, plenty of sauce and thin slices of red onion. Bake in the oven for 5-10 minutes until bubbling and hot. Scatter with coriander leaves.