Place the oven rack about 7 inches from the broiler and preheat the broiler. Place the peppers on a baking sheet and char them under the broiler, turning them often with tongs so that they blister all over, about 20 minutes. Let the peppers stand until cool enough to handle. Remove the charred skin, cut the peppers in half, and remove the seed pods.
Combine the lemon juice, vinegar, olive oil, garlic, and salt in a saucepan and heat just to boiling over medium heat.
Have ready 3 scalded pint (500 ml) jars and their bands. (To scald, simply dip the jars in boiling water. You don't need to sterilize the jars, as you will be processing them for over 10 minutes.) Simmer new lids in a small pan of hot water to soften the rubberized flange.
Pack the peppers into the jars and pour the marinade over them. Using a butter knife, pop any air bubbles in the jars. See that the garlic slices are distributed evenly. Be sure to leave 1/2 to 3/4 inch of headspace in the jars, or your seal might fail. (Why? Because the peppers puff up some during the water bath process, and if there is not enough space for the air to be pushed out of the jar by the heat, the pressure will push out oil as well and the seals won't stick.) Wipe the rims, place on the lids, and screw on the bands fingertip tight.
Process the peppers in a boiling water bath for 15 minutes. Turn off the heat and allow the jars to sit in the water for 5 minutes, then remove the jars and let them rest for 4 to 6 hours. Check the seals and store in a cool, dry place for up to a year.