Preheat oven to 350 degrees F (180 degrees C).
Heat a large skillet on medium heat.
Pour in half of the Extra-Virgin Olive Oil (2 tablespoon) and saute together the Zucchini (1 cup), Leek (1/3 cup), Celery (1/3 cup), and Garlic (1 teaspoon) until the garlic starts to brown.
Add the rest of the Extra-Virgin Olive Oil (2 tablespoon), the Fresh Parsley (2 tablespoon), Dried Marjoram (1/2 teaspoon), Salt (1/2 teaspoon), Ground Black Pepper (1/4 teaspoon), and then the Fresh Baby Spinach (12 ounce). Stir until spinach is wilted, around 5 min. Remove from heat.
Add Mozzarella Cheese (2 cup) and White Rice (1 cup) to skillet, stirring until cheese is melted and mixed in. Remove from heat.
Cut off the tops off of the Bell Pepper (4). Remove all seeds and veins from their centers. Place peppers upright in a small baking dish (just big enough that they fit snug together).
Fill the peppers with the cheese and spinach filling, then place into the oven and bake uncovered for 15 minutes.
Top each pepper with the Parmesan Cheese (1 cup) and bake for another 10 minutes.