Preheat oven to 400 degrees.Fill a baking dish with 1/2 cup water.

In a small bowl, mix together the garlic powder, chili powder, cumin, paprika, salt and pepper. Sprinkle generously over both sides of the chicken breasts, then place them in the baking dish.

Roast chicken in oven for about 20-25 minutes, or until the chicken breasts are cooked through. Remove from oven, transfer chicken to a large bowl, and shred using two forks. Set aside. Reduce oven heat to 375.

In a medium sized bowl, mix together the corn and black beans.

To prepare the casserole, start by misting a 9 x 13 casserole dish with nonfat cooking spray or an olive oil mister.

Add about 1/2 cup of enchilada sauce to the bottom of the casserole dish. Spread evenly with the back of a spoon. Top with a layer of 8 tortilla halves, so that the entire dish is covered.

Now sprinkle about 1/3 of the black bean corn mixture on top of the tortillas. Follow with about 1 cup of shredded chicken, and then about 1/3 of the cheese. Top with a sprinkle of green onions and cilantro.

For the second layer, start with 8 tortilla halves, then about 1 cup of enchilada sauce, then the black beans and corn, then the chicken, then these cheese, then green onions and cilantro.

For the third layer, start with 8 tortilla halves, then the remainder of black beans and corn, then the remainder of the chicken, then the remainder of enchilada sauce, but reserve the cheese, cilantro and green onions.

Cover and place in oven for about 20 minutes. Remove pan and take off the aluminum foil. Sprinkle the top of the enchiladas evenly with the remaining cheese, then return to the oven (uncovered) and bake for 10 minutes or until the cheese is melted. 

Remove pan, and top with the remaining green onions and cilantro. Let cool for about 5-10 minutes, then cut into 8 equal pieces.