In a medium saucepan, heat olive oil over medium heat and cook onions for about 5 minutes until softened. Add garlic and cook for an additional minute. .
Add black beans, water, oregano, and cumin. Bring to a boil then reduce to a simmer until most of the liquid has evaporated, about 15 minutes.
Season with salt and pepper to taste. Mash with a fork or potato masher, and set aside for later use.
Meanwhile, preheat oven to 350F.
Coat a 8” x 12” baking dish with cooking spray and cover the bottom with ½ cup of enchilada sauce.
Place some bean mixture and corn in the center of tortilla, roll up and place into the prepared baking dish, seam-side down. Repeat with remaining tortillas.
Pour remaining enchilada sauce over enchiladas and top with shredded cheese. Bake for 30 minutes until the cheese is melted and bubbly.
Serve immediately with cilantro and sour cream if desired.