Preheat your oven to 350°F (175°C).
In a large skillet, sauté the diced onions and bell peppers until they begin to soften.
Add the diced tomatoes, corn, black beans, diced green chilies, chili powder, cumin, garlic powder, salt, and pepper. To allow the flavors to meld together cook for another 5 minutes.
In a separate bowl, combine the sour cream and vegetable broth, stirring until smooth.
Gently coat a 9x13-inch baking dish with a thin layer of cooking spray. Place half of the corn tortillas in the bottom of the dish, slightly overlapping them.
Layer half of the vegetable mixture over the tortillas, followed by half of the sour cream mixture and half of the shredded cheddar cheese.
Repeat the layers with the remaining tortillas, vegetables, sour cream mixture, and cheese.
Place aluminum foil over the baking dish and then bake for 30 minutes. Next, take off the foil and continue baking for an extra 10-15 minutes until the casserole becomes bubbly, and the cheese achieves a golden brown hue.
Garnish with fresh cilantro if desired.