Lay each of the onion halves, cut sides down, on a 16-inch
square of aluminum foil. Nestle the garlic cloves between the
onions. Drizzle a couple tablespoons of oil over the onions
and garlic. Fold up the sides of the foil and seal the
packet. Place the packet over direct medium heat, with the
lid closed, until a knife inserted through the foil
slides easily in and out of the onions, 20 to 30
minutes, turning the package once or twice.
Carefully remove the package from the grill with
tongs and let cool to room temperature.
Open the packet and remove and discard the skins
and hard stem ends from the onions and garlic.
Place the roasted onions and garlic in the bowl
of a food processor fitted with a metal blade. Pulse
until almost puréed. Add all the remaining dip
ingredients and process until quite smooth. Adjust the
seasonings, if desired.
Lightly brush the pita on both sides with oil. Working
in batches of 3 or 4 pitas at a time, grill them over direct
medium heat until crisp and toasted, 2 to 4 minutes, turning
frequently. Cut each pita into wedges. Serve with the dip.