Step 1

In a food processor, pulse garlic to chop, then add lemongrass and pulse until finely chopped. Add shallot and pulse to create a fine paste. Pulse in oil, soy and fish sauces, and brown sugar until smooth.

Step 2

Butterfly pork loin: Place pork on a cutting board vertically (with short sides at top and bottom). Using a large, sharp knife, and starting at top, cut lengthwise down the center, almost all the way through but leaving a hinge of about 1/2 inch. Unfold, as if opening a book.

Step 3

With knife blade parallel to cutting board, slice through left side of loin, opening meat as you go, and again leaving a hinge. Repeat with right side. If needed, pound loin to an even thickness with a meat mallet. Season with salt, then rub half of lemongrass paste all over meat. Re-form into original shape, tie with kitchen twine at 2-inch intervals, and wrap in plastic. Refrigerate at least 8 hours and up to 1 day. Bring to room temperature 1 hour before grilling.

Step 4

Prepare grill for direct- and indirect-heat cooking. Remove pork from plastic; place over indirect heat, cover, and cook, maintaining a temperature of about 400°F, about 20 minutes. Brush with remaining lemongrass paste and continue cooking, covered, until a thermometer inserted into thickest part of pork registers 135°F, about 15 minutes.

Step 5

Transfer to direct heat and cook, uncovered, turning frequently, until charred in places and thermometer registers 138 ̊F, about 5 minutes more. Let pork stand about 10 minutes, then thinly slice and serve with pickles, chili sauce, lettuce, and herbs.