Halve all the vegetables and brush with the oil. Sprinkle with salt and pepper. Light a grill and oil the grate. Grill the avocados, lemons, 
tomatoes and onion cut side down along with the whole chiles over moderate heat until charred but not falling apart. Start with the avocado, tomatoes and jalapeño- about 10 minutes. Then add the onions for about 8 minutes. Grill lemons for about 3 minutes. As the items finish cooking, transfer them to a cutting board 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 pepper, 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 lemons over the guacamole and season with salt and pepper; mix gently. I like a coarse guacamole so don't smash too much- But hey if you like it not coarse smash away.