Heat olive oil in a large skillet over medium heat. Add onion and cook until softened, about 5 minutes. Add garlic and cook for 1 minute more.
Stir in spinach, black beans, 1/2 cup Monterey Jack cheese, cumin, salt, and pepper. Cook for 2-3 minutes, until heated through.
Warm tortillas slightly to make them pliable.
Spread about 1/4 cup of the spinach mixture down the center of each tortilla. Roll up and place seam-side down in a lightly greased 9×13 inch baking dish.
In a bowl, whisk together salsa verde and sour cream. Pour evenly over the enchiladas.
Sprinkle with the remaining 1/2 cup Monterey Jack cheese.
Bake for 20-25 minutes, or until heated through and cheese is melted and bubbly.
Garnish with fresh cilantro before serving.
Notes
For a spicier enchilada, add a pinch of cayenne pepper to the spinach mixture.
If you prefer a richer sauce, you can add a bit more sour cream or a dollop of Mexican crema.
Feel free to add other vegetables like corn or diced bell peppers to the filling.