Gently heat your chapatis in the oven or microwave until warm and soft. Cover half of each chapati with 1 tablespoon of Greek yogurt and 1 teaspoon of mango chutney. Lay the bacon on top, followed by a few stalks of coriander. Sprinkle over the nigella seeds, dividing them evenly between the 4 wraps, and finish with a sprinkling of chilli flakes to taste. Fold the other half over the top, then fold again into a chunky triangle to serve.