Preheat oven to 400?. Cook Rice a Roni according to the directions.
Remove the stems and gills on the portabellas. Clean the portabellas with a paper towel, removing any dirt.
Place 2 tablespoons of olive oil in a bowl. Brush the top (cap) of the portabellas with olive oil sprinkle with salt and pepper. Flip the mushrooms over and brush with olive oil and sprinkle with salt and pepper. Bake for 10 minutes. Remove from oven and reduce heat to 350?.
While the portabellas are cooking, put 2 tablespoons of olive oil and the minced garlic in a skillet on medium heat and add the baby spinach. Cook until the spinach is wilted.
Mix rice, spinach, and ricotta cheese. Top the portabellas with the rice mixture, distributing evenly among the mushrooms. Top with parmesan cheese and bake for 30 minutes.