Heat a ridged grilling pan (or you can use a large saute pan lined in aluminum foil) over high heat and arrange the tomatoes, onion slice, garlic cloves and poblano chile(s) in a single layer. Roast everything, turning occasionally, until the tomatoes, onion, garlic and poblano chile are all soft and blackened in spots—about 10 minutes for the garlic, 15 minutes for the chiles and 20 minutes for the tomatoes and onions. Cool all the roasted vegetables until handleable, then peel the tomatoes, chile(s) and garlic. Pull out the stem and seed pod from the chile(s), then rinse briefly to remove all the seeds and bits of skin; slice into 1/8” strips. In a large food processor, make a coarse puree from the onion and garlic. Add the tomatoes and their juice, then process into a thick, coarse-textured sauce. Transfer to a bowl and stir in the chile strips, lime juice, cilantro and salt. If salsa is too thick, drizzle in a little water.