Kebabs, part 1: In a mixing bowl, combine ground lamb, milk, and bread cubes; mix until the bread starts to break apart, about 30 seconds. Add the diced onion, smoked paprika, cumin, powdered milk, baking soda, and salt; mix again to combine. Mix in the black pepper, and the kebabs are ready to be cooked.
Kebabs, part 2: Place flour in a small bowl. Divide meat mixture into three equal portions. Gently pat each one into a slightly flattened ball and dredge in flour to coat; remove excess flour. Meanwhile, heat oil in a skillet over medium heat. When the oil is hot and shimmering, add the kebabs. Cook 8–10 minutes, turning once, until kebabs are golden brown on all sides, firm to the touch, and slightly pink in the center. (If they need more time, cover the skillet for 2-3 more minutes and let the steam finish them off.)
Tahini Sauce: In a bowl, whisk together tahini, half of the lemon juice, and salt. Thin out with water, 1 tablespoon at a time. It will look like it’s seizing up, but keep stirring, about 30 seconds, and it'll become a smooth and creamy sauce.
Assemble: Place the kebabs on a plate and top them with arugula, followed by remaining lemon juice, olive oil, and a few tablespoons (or more) of tahini sauce. Serve immediately.