Thinly slice the onion, chilli and garlic, dice the aubergine. Cut the buns in half.
Heat the oil in a pan and gently sauté the onion, chilli and garlic. Add the aubergine, cumin and oregano, stir, then add the tomatoes. Put the lid on and gently sweat until the aubergine & tomatoes are tender.
Season with salt and pepper, then add the balsamic vinegar and spinach or parsley. Turn up the heat and let it bubble for a couple of minutes, stirring, until the sauce becomes sticky and the spinach has wilted.
Remove from the pan to a bowl, cover to keep warm (or put aside until needed).
Cut the halloumi into 4 slices. Wipe out the pan, add some oil and brown the cheese on both sides for a couple of minutes. (Alternatively, you can barbecues or grill the slices)
Meanwhile toast or grill your buns.
Spoon the aubergine mixture on the bottom half of your bun, top with two halloumi slices then cover with the other half of the bun.
Serve immediately.