Preheat your oven to 375°F (190°C). Lightly grease a 9x13 inch baking dish. Dice the yellow onion and zucchini, and mince the garlic cloves. Rinse and drain the black beans.

Heat the olive oil in a large skillet over medium heat. Add the diced onion and cook for 3-4 minutes until softened. Stir in the minced garlic and cook for another minute until fragrant. Add the diced zucchini, salt, and pepper, cooking for 8-10 minutes until the zucchini is tender and most of its liquid has evaporated. Stir in the drained black beans and undrained green chiles; cook for 2-3 more minutes, then remove from heat.

Pour about 1/2 cup of the enchilada sauce into a shallow dish. Briefly dip each corn tortilla into the sauce to soften it, or alternatively, warm them in the microwave for 30 seconds to 1 minute between damp paper towels until pliable. This makes them easier to roll without cracking.

Lay a softened tortilla flat. Spoon about 1/4 cup of the zucchini and black bean filling down the center, then sprinkle with about 1 tablespoon of shredded cheese. Roll up the tortilla tightly and place it seam-side down in the prepared baking dish. Repeat with the remaining tortillas and filling until the dish is full.

Once all enchiladas are assembled in the dish, pour the remaining enchilada sauce evenly over the top. Sprinkle the remaining 1.5 cups of shredded Monterey Jack cheese generously over the sauce.

Bake for 20-25 minutes, or until the sauce is bubbly around the edges and the cheese is melted and lightly golden.

Let the enchiladas rest for 5 minutes before serving to allow them to set. Serve hot!