Kuchela is far more complex and less assertive than the sort of mango pickle you might pick up at the chutney bar at Patel's. It's made from shredded green mangoes, garlic, Scotch bonnet peppers, vinegar, mustard oil, salt, brown sugar, and a spice blend, or amchar, of cumin, coriander, black pepper, fenugreek, and mustard. It's typically used in curries, rice and beans, on roasted stuff, and with the Trinidadian specialties dhal puri roti and buss up shut.
But you can put it on any damn thing you like. I can't possibly express its utility more lyrically than Calypsoist Remy RemBunction:
Short of making your own you can find 13.5-ounce jars of Matouk's kuchela for $4.49 at:
Old World Market, 5129 N. Broadway, 773-989-4400