Combine the water, salt, and butter in a pot and bring to a boil. Pour the water over the rice in an oven-safe pan, stir together, and cover the pan with aluminum foil.
Bake the rice for 1 hour. When done, remove the foil and fluff the rice with a fork.
For the chicken
While the rice is cooking, season the chicken with lemon juice, spices, and garlic. Let set for thirty minutes to absorb the seasonings.
Heat the olive oil in a pan and add the onion. Saute until translucent and soft, then add the chicken and cook until done.
Drizzle the tahini sauce over the chicken. Serve the chicken, onions, and rice over the spinach.