Preheat your oven to 375°F (190°C). Lightly grease a 9x13-inch baking dish.

Warm the tortillas. Stack them, wrap in a clean towel, and microwave 30–45 seconds until pliable. This keeps them from cracking and helps them soak up flavor.

In a skillet over medium heat, warm the oil. Add the onion and cook 3–4 minutes until softened. Stir in the garlic and cumin for 30 seconds, just until fragrant. Remove from heat.

In a large bowl, mix the shredded chicken, cooked onion mixture, 1 cup salsa verde, 1/2 cup sour cream, half the cheese, cilantro, lime juice, and a pinch of salt and pepper. If using beans or corn, fold them in now.

Spread 1/2 cup salsa verde over the bottom of the baking dish. Tear or cut 4 tortillas into halves or quarters and arrange them in a single layer to mostly cover the bottom.

Spoon half the chicken mixture over the tortillas and spread it out. Drizzle with a few tablespoons of salsa verde.

Add another layer of tortillas, then the remaining chicken mixture, then a light drizzle of salsa verde.

Top with a final layer of tortillas. In a small bowl, whisk the remaining 1/2 cup sour cream with a few tablespoons salsa verde to thin it slightly. Spread this over the top layer.

Sprinkle the remaining cheese evenly over the top.

Cover loosely with foil and bake for 15 minutes. Remove the foil and bake another 10–12 minutes, until the cheese is melted and bubbling and the edges are lightly browned.

Let the casserole rest 10 minutes before slicing. Top with extra cilantro and a squeeze of lime if you like. Serve with avocado and more salsa verde.