How to Make It
In a large bowl, gently toss the avocados with the lime halves, tomatoes, chiles, red onion slices, the 3 tablespoons of oil and a generous pinch each of salt and pepper.
Light a grill and oil the grate. Grill the avocados, limes, tomatoes and onion cut side down along with the whole chiles over moderate heat until charred but not falling apart, about 3 minutes for the limes, 8 minutes for the onion and 12 to 15 minutes for the avocados, tomatoes and chiles. As the items finish cooking, transfer them to a work surface and let cool. Scoop out the avocado flesh and coarsely chop; transfer to a large bowl. Remove the seeds and stems from the tomatoes and chiles, finely chop and add to the bowl. Finely dice the onion and add to the bowl along with the cilantro and garlic. Squeeze the grilled limes over the guacamole and season with salt and pepper; mix gently. Serve with tortilla chips.