Spread 1 cup of the salsa verde in an even layer across the bottom of a 12-inch cast iron skillet (or a 9x13-inch casserole dish).
In a separate small skillet set over medium-low heat, heat 1/4 cup of salsa verde. Working one at a time, heat each tortilla in the warm salsa verde until just softened, about 30 seconds per side. Transfer the softened tortilla to a plate and fill with about 2 tablespoons of chicken filling. Gently roll the tortilla, then lay seam side down in the prepared skillet. Repeat with the remaining tortillas and filling, adding more salsa to the pan as needed.
Pour the remaining salsa verde over the enchiladas, then sprinkle with the cheese.
Transfer the enchiladas to the oven and bake, uncovered, until the cheese is hot and bubbly, 8 to 10 minutes.
Remove from oven and garnish with cilantro, diced onion, and avocado (if using). Serve with lime wedges and enjoy!