Trim the aubergines, then slice lengthways into thick slices. Mix the cumin, ground coriander and garlic into the oil, then lightly brush both sides of each aubergine slice with the flavoured oil, reserving the remaining oil.
Heat a large, heavy-based frying pan over a medium-high heat and cook a third of the aubergine slices for 3–4 minutes, turning once, until softened and lightly browned. Remove from the pan and cook the remaining batches of slices in the same way.
Place the warm aubergine slices in a food processor with the lemon rind and juice and the reserved flavoured oil. Whizz until almost smooth but with a little texture. Transfer to a bowl, then mix in the fresh coriander and season with a little salt and pepper.
Griddle or toast the pitta breads until golden and warm, cut into strips and serve with the dip.