Place an 11- or 12-inch tagine or cazuela or Dutch oven on a heat diffuser, if you have one, over medium-low heat. Add the grated onion, butter, saffron water, spices, salt, 3/4 cup of the cilantro, and hot water.
Slowly raise the heat and bring to a boil, then reduce the heat to medium-low, cover, and simmer gently to blend the flavors, about 10 minutes.
Add the kefta, or meatballs, to the sauce and poach, covered, for 30 minutes, turning them midway through the cooking.
Add the lemon juice to the sauce. Taste and correct the seasoning with salt and pepper. Transfer the hot pot to a wooden surface or a folded towel placed on a serving plate and garnish with the remaining 1/4 cup cilantro.
Spoon the kefta and sauce directly from the pot onto plates, with warm slices of toasted bread for mopping up the sauce.