Heat 2 tablespoons of oil in a frying pan over medium heat. Add the spinach and cook uncovered until the spinach is completely wilted, stirring occasionally. Squeeze out all of the excess liquid from the spinach in a colander with the back of a spoon. Add the cilantro, garlic, sundried tomato, salt and pepper. Mix well and set aside.
Preheat the oven to 400 degrees F. Rub the olive oil all over the outer part of each portobello mushrooms and place them on a oven tray.
Spoon 1/4 cup ricotta cheese in each mushroom cap.
Spread a layer of spinach mixture.
Then top with shredded mozzarella cheese.
Bake until cheese is melted and mushrooms are tender, about 18-20 minutes. Serve the Stuffed Portobello Mushrooms immediately.