Whisk the marinade ingredients and add the London broil. Let sit for at least four hours, ideally overnight.

Stir all ingredients. Start with one tablespoon harissa and add more for heat.

Toss ingredients and let sit while the meat cooks.

Preheat the grill.

Cook the London broil for three to four minutes per side for medium rare. Pull it before it’s well done. This is a lean cut, and it turns tough if you overcook it. Rest for five minutes, then slice it thinly against the grain.

Toss the scallions in a little olive oil and lay them on the grill grates for one to two minutes, until charred and soft. Roughly chop.

Lower the grill to medium-low. Brush a light layer of oil on the sourdough and lay it right on the grates until golden.

Spread harissa mayo on two slices sourdough bread, then layer the beef, scallions, and a pile of slaw. Cover with the second slice and press lightly. Slice on the diagonal.

No grill? Sear the London broil in a screaming-hot pan for two to three minutes per side, and char the scallions in the same pan.