Place a large cast-iron skillet over medium-high heat and heat until just beginning to smoke. Rub the corn with olive oil, then carefully lay into the pan. Cook until charred in patches all the way around and golden brown, 20 to 25 minutes, turning every 5 minutes. Remove and let cool.
For the dressing: Meanwhile, whisk together the lime juice, cumin, cayenne, cardamom, chaat masala and salt and black pepper to taste. Slice the kernels off the cobs and tumble into a big bowl. Add the tomatoes, mint and cilantro. Toss with the dressing, and taste for seasoning. Serve!