Preheat oven to 400 degrees F (200 degrees C).
Grate the Monterey Jack Cheese (1 cup). Grate the Parmesan Cheese (1 cup).
Grate the Garlic (1 clove).
Thaw the Frozen Spinach (10 ounce). Drain by putting it in to a kitchen towel, then squeezing it.
If using jarred Artichoke Hearts (1 cup), drain the artichokes fully.
Chop the Artichoke Hearts.
Add the Cream Cheese (1 package), spinach, and chopped artichokes to a bowl and stir to combine.
Add in the Garlic and Monterey Jack Cheese. Add salt and pepper, then mix well to create the filling. You'll use the Parmesan cheese later.
Clean the Portobello Mushroom (12) and take out the stems.
Bake the portobello mushrooms, with the tops up on baking sheet with a rack on it for about 15 minutes. They should be beginning to slump but aren’t fully cooked.
Flip the portobello mushrooms (12) over, fill each mushroom with some of the filling. Sprinkle parmesan cheese (1 cup) on top and put back in the oven at 425 degrees F (220 degrees C). Season with Salt (to taste) and Ground Black Pepper (to taste).
When done, the mushrooms can be served immediately, or set aside to cool and then stored.