Turn the oven to the broil setting.
Cook the spinach in the microwave or on the stove according to package directions.
Using a spoon, scrape the "gills" from the mushroom caps. Lightly clean the top of the mushroom with a dry paper towel, gently rubbing the cap but be careful not to break the mushroom.
Line th mushroom caps upside down on a baking sheet.
Once the spinach is cooked, divide it into 4 equal servings and add to the base of the mushroom.
Divide the chopped artichokes into 4 equal portions and add over top the spinach.
Sprinkle 1/2 cup of parmesan cheese to the top of each mushroom.
Lightly drizzle each mushroom cap with olive oil, adding about two teaspoons of oil to each mushroom over the cheese.
Broil in the oven for 3-4 minutes, until the parmesan begins to melt.