Heat the olive oil in a large cast-iron skillet over medium heat. Add the garlic and light green and white scallions and quickly saute, taking care not to burn the garlic, for 2 minutes. Stir in the green chiles and chili powder and cook for 1 minute. Stir in the roasted veggies, black beans, spinach and corn. Season with salt and pepper and add the salsa. Increase the heat to medium-high and let cook until the spinach and corn thaw and the sauce gently simmers, 10 to 12 minutes. Add 1/4 cup water if necessary, to thin out the sauce.
Top with the cheese, then cover and let cook until the cheese is fully melted, about 3 minutes. Top with the scallion greens and any other optional garnish. Serve from the skillet with the tortillas.