Heat oven to 200C/180C fan/gas 6.
Toss the sweet potatoes with chilli,
1 tsp oil, cumin seeds, garam masala
and plenty of seasoning on a roasting
tray. Roast for 25-35 mins, turning
wedges halfway, until tender and golden.
Meanwhile fry onion in remaining oil
for a few mins until partly softened, stir
in the lime juice and sugar with some
seasoning, then turn off the heat.
Warm chapatis following pack
instructions, then assemble by adding
a couple of wedges of sweet potato to
each, followed by a scattering of onions,
a dollop of yogurt and a small handful of
coriander leaves. Roll up and eat.