Line a large baking sheet with parchment paper. At the grill, have another clean tray ready for when the corn and onion are finished. Also have at the grill a large bowl and plastic wrap. These will be for when the tomatoes and peppers are finished.
Place the tomatoes, green and red bell peppers, onion slices, jalapeño, poblano pepper and ears of corn onto the lined baking sheet.
Use a silicone brush to brush the vegetables oil over all the vegetables, turning them to coat all sides.
Heat the grill to medium. Make sure the grates are clean and free of debris.
Place the oiled veggies directly onto the grates. Adjust the flames of the grill so that they are just under the veggies and not charring them. Close the cover.
Turn the veggies every few minutes to cook them evenly.
After 7 minutes remove the tomatoes, bell peppers, jalapeño and poblano pepper and place them into the large bowl. Cover the bowl tightly with plastic wrap: they will steam in the bowl. Continue grilling the onion and corn.
Grill the onion and corn for another 8 minutes. They should be evenly roasted, with some grill marks and just beginning to turn soft from cooking over the heat. Place them on the clean, waiting tray. Bring the tray and the bowl inside to the prepping area.
Once the veggies in the bowl have steamed for about 15 minutes, the skins can be removed. Cut the stem ends off the peppers and slice them in half lengthwise. Scoop out and discard the seeds, membranes and extra liquid. Flatten the pepper halves, then peel off and discard the skins. Slice the peppers into small pieces and place them into a large clean bowl.
Slice the tomatoes in half lengthwise. Scoop out and discard the seeds, pulp and extra liquid. Peel off and discard the skins. Chop the tomatoes into small pieces and add them to the bowl.
Chop the red onion into small pieces and add to the bowl with the other vegetables.
Slice the corn off of the cobs: stand a cob vertically on its flat end on a cutting board. Hold it at the top and carefully slice straight down with a sharp knife to remove the kernels. Rotate and repeat around the cob. Add the corn and liquid from the corn kernels to the bowl.
Stir the vegetables together. Add to the bowl the lime juice, cilantro, salt and pepper and stir to combine the ingredients thoroughly.
The salsa can be served immediately or allowed to refrigerate for about 30 minutes to let the flavors meld.
The salsa can be refrigerated, tightly covered for up to 4 days. Makes about 5 cups.