Preheat the oven to 400°F.
Place the parsley and onion in a food processor and pulse until very finely chopped. Drain off any excess moisture.
Transfer the parsley and onion to a large bowl. Add the ground beef, Lebanese seven spice, sumac, salt, and black pepper. Mix gently until evenly combined.
Press the kafta mixture into an even layer in the bottom of a 9 x 13-inch baking dish. Bake for 20 to 25 minutes, or until the kafta is cooked through and reaches an internal temperature of 160°F.
While the kafta bakes, rinse the sliced potatoes, drain well, and pat dry. Air-fry in batches at 400°F for approximately 15-20 minutes, turning halfway through, until lightly golden and almost tender. Cooking time will depend on the thickness of the slices and the air fryer. Alternatively, deep-fry the potato slices in neutral oil until lightly golden, then drain on a paper towel-lined plate.
Carefully drain any excess fat or liquid from the cooked kafta. Cut the kafta into serving portions directly in the baking dish.
Arrange the potatoes over the kafta. Top with the sliced tomatoes and red and yellow bell peppers.
In a large measuring cup or bowl, combine the hot water, tomato sauce, salt, and black pepper. Pour evenly over the kafta and vegetables.
Return the dish to the 400°F oven and bake for another 20 to 30 minutes, or until the sauce is simmering, the vegetables are tender, and the potatoes are cooked through.
Let the dish rest for 5 to 10 minutes. Serve warm with Lebanese vermicelli rice and spoon plenty of tomato sauce over each serving.