Rinse and drain the rice without soaking it. Clean the mushrooms and cut them into slices. Heat the oil in a pot and fry the chopped leeks and garlic, cut coarsely. Once soft, add the mushrooms and sauté until they soften.
Add the rice and stir it until braised. Add 1 cup water, season with spices to taste and allow the rice to absorb the liquid. Transfer to a large baking dish, add 5 cups hot water and put the dish to bake until the rice swells.
Bake in preheated oven at 365°F (185°C). Serve with chopped green onions.