Portobello, Spinach, and Smoked Gouda Mac and Cheese



6 oz large portobello mushrooms
cooking spray
12 oz whole wheat pasta (I used fusille because my store did not have macaroni)
1 Tbs unsalted butter
1 Tbs all-purpose flour
1-1/2 cup lowfat milk
1 tsp Dijon mustard
1 tsp kosher salt (plus additional for the pasta water)
pinch fresh cracked pepper
4 oz smoked Gouda cheese, shredded and divided
1 cup fresh spinach leaves, chopped
1 Tbs panko breadcrumbs
1 Tbs freshly grated Parmagiano-Reggiano cheese
1/2 tsp extra virgin olive oil