To prepare the spice blend, dry roast the coriander and cumin seeds. Cool, add the chilli flakes and grind to a fine powder. I used the entire blend as I was wanted a good kick of the spices but you can add just enough to suit your taste preferences.
If you are using a food processor, throw in all the ingredients for the burger including the spice blend; or finely chop the onion and aromatics and then mix all ingredients together for the burger patties.
Form the mince into circular patties and keep aside. Again, the thickness of the patty is entirely upto your preferences; I make thick ones and for a kilo of mince, made 10 patties.
Heat a grill pan, brush with oil and grill the burgers till done; flip around after giving a couple of minutes on each side to get the char grilled marks. Rest the burgers for at least two minutes before preparing the sandwich.
Grill the pineapple slices (make sure the grill is smoking hot to instantly caramelize the sugars which keeps the crunch intact and seals the juices inside; on low heat, the pineapple slices go limp and soggy).
Cut the burger buns in half and grill for that extra crunch.
To assemble the sandwich, place shredded lettuce on the bottom half of the bun and layer up – patty, barbeque sauce, pineapple slice, tomato, onions and coriander leaves.