To make the naan, Sift the flour, salt and baking powder into a large bowl.
Mix the sugar, milk, egg and 3 tablespoons of the oil together.
Make a well in the centre of the flour mix and add the liquids.
Mix well and then turn onto a floured surface and knead well.
Add the rest of the oil and continue kneading until the dough is smooth and all the oil is incorporated.
Place back into the bowl, cover and leave to rest for 2-3 hours.
Divide into 8 balls (slightly smaller than tennis balls), roll and shape them into circles.
Place on a baking sheet and set aside. Pre-heat the oven to it's hottest setting.
To make the patties, combine all the ingredients and mix well. Form the mixture into patties and set aside.
To make the raita, combine all the ingredients. Season to taste and set aside.
Cook the patties in a hot pan until cooked through.
Place the naan discs into the oven and allow to bake until golden brown and puffed up. Flip over and allow to brown on the other side. Remove from the oven and brush with butter.
Serve the patties on the naan bread, top with the raita and the sliced onion.
Notes
The prep time might seem extravagant but I've allowed 3 hours because of the resting time for the naan dough.