For the sauce:
In a bowl, mix together the first five ingredients.
Taste the mixture, then add lemon juice, salt and pepper, to your liking. Cover and place the bowl in the refrigerator.
This is best made ahead of time so it can chill for a day or so while the flavors meld. Add the chopped cilantro before serving.
For the peppers:
Heat the olive oil in a heavy pan (a cast-iron skillet works great) until very hot but not smoking; water should readily sizzle.
Cut a slit in the tip of each pepper. Add the peppers and cook until blistered and at least as black as they are green, carefully turning with tongs to darken all sides—about 10 minutes.
Transfer to a serving plate, sprinkle with salt and squeeze lightly with lemon juice. Serve with the chilled sauce.