Remove the stems from the portobello mushrooms and set them aside.

In a large pot, bring water to a boil. Add the mushroom caps and cook for 2-3 minutes to soften them slightly. Remove the mushrooms from the pot and set them aside to cool.

In a frying pan, heat the olive oil over medium heat. Add the chopped onion and minced garlic, and sauté until softened.

Finely chop the mushroom stems and add them to the frying pan. Cook for a few minutes until the mushrooms release their moisture.

Add the diced tomato, tomato paste, cooked rice, lemon juice, ground cumin, ground coriander, ground cinnamon, salt, and pepper to the frying pan. Stir well to combine all the ingredients.

Cook the mixture for about 5 minutes, allowing the flavors to blend together. Remove from heat and let it cool.

Preheat the oven to 180°C (350°F).

Stuff the cooled mushroom caps with the rice mixture, pressing it firmly into each mushroom.

Place the stuffed mushrooms in a baking dish and cover the dish with aluminum foil.

Bake for about 45 minutes, or until the mushrooms are tender and the filling is heated through.

Remove from the oven and garnish with fresh parsley.

Serve the vegan Egyptian Hamam Mahshi as a main dish with a side of salad or rice.