Preheat oven to 400F. Clean the portobello mushrooms, removing the stems and using a spoon to scrape the gills out from inside the caps.

Brush four-fifths of the olive oil onto the mushroom caps and sheet pan. Season with salt and pepper and bake for 10 minutes. If the mushrooms have any water in them, just dab it away with a paper towel.

Heat the remaining olive oil in a skillet over high heat. Add the artichoke hearts and spinach and let cook until the spinach leaves are mostly wilted.

Add the cream cheese to the pan, stirring until mostly melted. Add the shredded parmesan. Remove from heat and season with salt and pepper, ensuring that the filling is thoroughly mixed.

Stuff the mushroom caps with the filling.

Top each mushroom with flaxseed meal and parmesan.

Bake for an additional 5 minutes, or until the topping is melted.