Gather all ingredients.
In a small mixing bowl add enchilada sauce.
Add flour to enchilada sauce.
Mix the flour and the enchilada sauce.
With a spoon, gently scrape out the gills of the mushroom caps.
Place the caps on onto the grill.
Coat the mushrooms in olive oil.
Sprinkle salt onto the caps.
Evenly spread 1/2 cup corn between the four caps.
Do the same as the previous step except with your 1/2 cup black beans.
Pour enchilada sauce directly onto the portobello caps.
Sprinkle and coat with mozzarella cheese. Turn grill on to high a cook for 10 minutes and make sure all cheese is melted.
Add some green onions to the top when the are finished cooking, and serve while hot!