Make marinade: The day before, mix mustard, parsley, and olive oil in a large bowl; add lamb and smear evenly. Seal meat in 2 large resealable plastic bags. For salsa, rinse parsley and mint, and spin dry; wrap in paper towels and seal in a bag. Chill ingredients in a cooler.
Build a fire (see “Campfire 101,” page 69) and let burn until you can hold your hand 5 in. above firepit grate only 5 to 7 seconds. Let meat come to room temp (1 to 2 hours).
Meanwhile, make salsa verde: Gather parsley and mint into a bundle and thinly slice. Put in a medium bowl and combine with remaining ingredients, seasoning to taste with fine sea salt.
Season lamb liberally with fine sea salt and pepper.
Set a charcoal cooking grate over firepit cooking grate. Grill lamb, turning often, un- til medium-rare (cut to test) or center registers 115° to 120° on an instant-read thermometer, 25 to 30 minutes. Transfer to a board and let rest a few minutes.
Slice lamb between bones, arrange on a platter, and sprinkle with flake salt. Serve with salsa verde and lemon wedges.
*Frenched lamb racks have meat cut away from rib ends. Garlic scapes are tender young flower stalks of garlic plants; find them at farmers’ markets in late spring to early summer.
DO YOUR RESEARCH. Before you go, check that your campground allows fires and you can bring in wood or buy it there. You’ll want large logs, twigs for tinder, medium sticks for kindling, a butane lighter, newspaper, grilling tongs and gloves, home charcoal grill grate, and paper towels and oil for cleaning grates.
TIME IT RIGHT. The perfect fire for cooking has low flames plus plenty of embers. It takes 1 to 11⁄2 hours to burn down to this stage.
BUILD THE FIRE. In a fire ring with cooking grate pushed away, make a log cabin with 6 large logs: 2 parallel to each other, 2 crisscrossed on top, and a third set like the first. Crumple newspaper into the center and add a handful of twigs. Make a tipi over the twigs with some medium sticks. Ignite paper. Gently fan fire until flames emerge.
START A FEEDER FIRE. Off to the side of the main fire, ignite a second, smaller one with just a few logs. Let fires burn.
ARRANGE AND ADJUST . Using tongs, spread a bed of embers with low flames under the cooking grate and in area needed for dutch oven cooking. As you cook, add fuel from feeder fire.
PUT IT OUT. Never walk away from a fire that’s still burning. When it’s down to cinders, spread the remains in the fire ring and douse with water.