Heat the BBQ or set the broiler to high.
Slice the onion into thick slices, leave the skin on. Give a light coating of olive oil.
Prick the skins of the tomatoes and place them on a foil-lined tray.
Husk and wash the tomatillos and place them on the tray as well.
Cut the top off the garlic, drizzle with olive oil and salt, and wrap in tinfoil.
Place the onion slabs, peppers, garlic, and tray on the BBQ or under the broiler. Roast off the vegetables, turning or flipping to get a consistent char.
Put the roasted peppers in a bowl, cover with saran wrap and set aside.
Remove the outer ring of the onions and give a rough chop and place in the food processor.
Remove the skins and seeds from the peppers, and squeeze the garlic out of the skin, and place in a food processor.
Remove the skins from the tomatoes, placing them and all the remaining ingredients into the food processor.
Blend until well mixed, then proceed to add anyadditional salt, seasonings, and lime juice according to taste.