Place the spinach into a microwaveable bowl, and heat on full until lightly wilted (mine took 50 seconds). Set aside to cool.
Chop the spring onions into 1/2cm rounds, and combine with the drained black beans, chopped coriander, and half of the grated cheese.
When the spinach is cool enough to handle, squeeze out any excess liquid, and add this to the filling mixture. Mix well.
To make the sauce, melt the butter in a large saucepan. Whisk in the flour until lightly browned, about 1-2 minutes. Gradually whisk in the chicken stock and cook, whisking constantly, until incorporated, about 1-2 minutes. Stir in the sour cream. Add the jalapeños and garlic powder and simmer unitl the sauce has thickened, about 2 minutes; season with salt and pepper, to taste. Remove from heat and stir in the cilantro.
To assemble the enchiladas, lay the tortilla on a flat surface and spoon 1/3 cup of the bean mixture in the center; sprinkle with cheese. Roll the tortilla and place seam side down onto prepared baking dish coated with 1/2 of the jalapeno cream sauce,. Repeat with remaining tortillas and bean mixture.
Pour remainder of the jalapeño cream sauce evenly over the top. Place into oven and bake, covered, until lightly golden and bubbly, about 20 minutes.