Diagonally cut sourdough bread into 6 slices (to make 3 sandwiches).

Make chutney by adding cilantro (stems and half of the leaves), chile (seeds discarded unless you prefer it extra spicy), lime juice, sugar, and salt into a food processor. Process this on high, slowly adding oil until it becomes an emulsion.

Make filling by roughly chopping the remaining half bunch of cilantro leaves and mixing them together with the yogurt and diced red onion with a pinch of black pepper.

Preheat the grill (or in our case, a cast iron grill). Spoon over the yogurt mixture on 3 pieces of toast and cover with the other 3 pieces to make sandwiches. Combine some oil with mustard seeds and brush over each side of the sandwich.

Grill sandwiches for a few minutes on each side, cut diagonally, and serve with cilantro chutney.