Preheat and prep. Heat your oven to 375°F (190°C).
Grease a 9x13-inch baking dish. Warm your enchilada sauce in a small saucepan until just steamy.
Sauté the aromatics. In a large skillet over medium heat, add 1–2 tablespoons oil. Cook the onion with a pinch of salt for 3–4 minutes, until translucent.
Stir in the garlic and cook 30 seconds until fragrant.
Add the veggies. Toss in the bell pepper, zucchini, and corn. Season with cumin, chili powder, smoked paprika, oregano, salt, and pepper. Cook 4–6 minutes until the veggies soften but still have some bite.
Wilt the greens. Stir in the spinach and cook 1–2 minutes until wilted.
Taste and adjust seasoning. Remove from heat.
Fold in the chicken. Add the shredded chicken to the skillet and mix gently so the flavors mingle. If the mixture looks dry, splash in 1/4 cup enchilada sauce.
You want a moist filling that’s not soupy.
Warm the tortillas. To prevent cracking, wrap tortillas in a damp paper towel and microwave 30–45 seconds. Alternatively, quickly toast each in a dry skillet for 10–15 seconds per side.
Coat the pan. Spread about 1 cup of enchilada sauce across the bottom of your baking dish. This prevents sticking and adds flavor.
Fill and roll. Place a warm tortilla on a board.
Spoon 1/4–1/3 cup of the chicken-veggie mixture along the center, sprinkle with a little cheese, then roll snugly. Place seam-side down in the dish. Repeat with remaining tortillas.
Sauce and cheese. Pour 1–1.5 cups of sauce evenly over the enchiladas, leaving some edges peeking through so they don’t get mushy.
Top with the remaining cheese in an even layer.
Bake until bubbly. Bake 15–20 minutes, until the cheese melts and the sauce bubbles around the edges. For a golden top, broil 1–2 minutes at the end, watching closely.
Finish and serve. Let the enchiladas rest 5–10 minutes so they set. Top with chopped cilantro and green onions.
Serve with lime wedges, avocado, and a dollop of sour cream or Greek yogurt.