How to Make It
Preheat oven to 325°F. Place garlic, shallot, oil, cumin seeds, 11/2 tablespoons kosher salt, and 2 teaspoons pepper in a mini food processor; process until mostly smooth, about 30 seconds. Rub spice paste all over lamb. Tie with kitchen twine, securing at 1-inch intervals to form a neat roast. Transfer to a wire rack set inside a large rimmed baking sheet.
Roast lamb in preheated oven until an instant-read thermometer inserted in thickest portion registers 135°F, 1 hour and 20 minutes to 1 hour and 30 minutes. Transfer lamb to a platter, and let cool to room temperature, about 1 hour. Cover with aluminum foil, and refrigerate until chilled, about 1 hour.
Meanwhile, place yogurt, cilantro, lime juice, jalapeños, scallion, anchovies, remaining 1 teaspoon kosher salt, and remaining 1/4 teaspoon pepper in a mini food processor; process until smooth, about 45 seconds.
Remove kitchen twine from lamb; discard twine. Cut lamb into thin slices, and sprinkle with flaky sea salt. Garnish with cilantro. Serve with sauce and pita bread.