Preheat the oven to 400°F (200°C). Lightly grease a 9x13-inch baking dish.
Heat olive oil in a large skillet over medium heat. Add the chopped onion and a pinch of salt. Cook for 5–7 minutes until softened.
Stir in the broccoli (or cauliflower) and red bell pepper. Reduce heat to medium-low, cover, and cook for 8–9 minutes until tender.
Add cumin and cinnamon. Cook for 30 seconds until fragrant.
Add the spinach in batches, stirring until completely wilted.
Transfer the vegetable mixture to a bowl. Add the black beans, ¼ cup shredded cheese, and about 2 tablespoons enchilada sauce. Season with salt and black pepper.
Spread ¼ cup enchilada sauce over the bottom of the baking dish.
Fill each tortilla with about ½ cup of filling, roll tightly, and place seam-side down in the baking dish.
Pour the remaining enchilada sauce over the Veggie Black Bean Enchiladas, leaving the ends slightly uncovered. Sprinkle with the remaining cheese.
Bake uncovered for 20 minutes. Broil for an additional 3–6 minutes if you prefer a golden cheese topping.
Let rest for 10 minutes before garnishing with fresh cilantro and serving.