Because these burgers use cooked lentils, they have a tender, moist center, which I love. Toasted walnuts give them a bit more texture and breadcrumbs help bind the ingredients together.
Cook the lentils: In a small saucepan, combine lentils with cold water to cover by 1 inch. Bring to a boil, and then reduce heat to a simmer. Cover partially and cook until the lentils are tender, but still hold their shape, about 20 minutes. Drain them in a colander and let them cool completely. This can be done up to one day ahead of time.
Toast walnuts: Preheat an oven or toaster oven to 350°F. Spread walnuts on a small baking sheet and bake until they turn golden brown and smell toasty, about 10 minutes. Let cool on the baking sheet completely. This step can be done in advance.
Process burger ingredients: In the bowl of a food processor, combine walnuts, breadcrumbs, scallions, parsley, garlic, tomato paste, Aleppo pepper, Baharat, 1 1/2 teaspoons kosher salt, and a generous grinding of black pepper. Pulse ingredients until they are finely ground. Add lentils and continue pulsing until they are incorporated into the mixture, leaving some whole.
Form the patties: In a large bowl, whisk the egg. Add the lentil mixture; mix until well combined. If time, chill the mixture for an hour, and up to overnight.Then, form the mixture into 6 large balls or, using about 2 tablespoons for each, 16 small balls. Flatten them with the palm of your hands and shape them into 3/4-inch-thick patties. Place them on a plate and refrigerate until you are ready to fry them.
Make Yogurt-Herb Sauce: In a small bowl, combine Greek yogurt, parsley, lemon juice, olive oil, and garlic. Whisk until smooth. Season to taste with salt and freshly ground black pepper.
Fry the burgers: Heat 1/4 cup oil in a large cast iron skillet over medium heat. Add burgers; cook, turning once, until crisp and browned, 5 to 6 minutes per side. Transfer to a paper towel-lined plate to drain.
Assemble and serve: Warm pitas or buns in a 300°F oven or toasted oven for 10 minutes. Slice in half. Spread about 1 tablespoon of Yogurt-Herb Sauce on the bottom of each pita half or bun. Layer in shredded carrots, sliced red onion, baby arugula, and burgers. Drizzle with more Yogurt-Herb Sauce.