Whisk ½ cup well-mixed tahini, 2 Tbsp. fresh lemon juice, ½ tsp. Diamond Crystal or ¼ tsp. Morton kosher salt, and ½ cup room-temperature water in a small bowl until smooth; set tahini sauce aside.

Heat 2 Tbsp. vegetable oil in a large skillet, preferably cast iron, over medium-high. Cook 1 large red onion, finely chopped, white and pale green parts of 6 scallions, thinly sliced, and 8 garlic cloves, coarsely chopped, stirring occasionally, until onion and scallions are tender and golden brown in spots, 8–10 minutes.

Add ¾ cup harissa (preferably thick), 1 tsp. crushed red pepper flakes (if using; you may not need it depending on your harissa and your own heat preference), remaining 1 tsp. Diamond Crystal or ½ tsp. Morton kosher salt, and ¼ cup water. Reduce heat to medium and cook, stirring often, until harissa is slightly darkened in color and oil beads on surface, about 5 minutes. Add 1 lb. ground beef (20% fat) and ½ cup water and cook, stirring often to break up meat, until water is mostly evaporated and beef is cooked through, 8–12 minutes. Remove from heat; mix in dark green parts of 6 scallions, thinly sliced. Season with more salt if needed.

Spread half of reserved tahini sauce in a large shallow bowl or over a platter; spoon beef mixture over. Top with a handful of salted pita chips and remaining tahini sauce, then ½ cup coarsely chopped mixed tender herbs (such as parsley, cilantro, and/or mint). Mix lightly to barely combine. Serve with more pita chips for crushing over.