SALSA VERDE:

Mix first 2 ingredients in large saucepan. Cover with water and bring to a boil. Reduce heat; simmer until soft, about 15 minutes. Remove from heat, let stand 15 minutes. Drain.

Coarsely chop tomatillo mixture, garlic, and cumin in processor using on/off turns. Add next 3 ingredients, blend until herbs are chopped and salsa is chunky.

Heat oil in heavy large saucepan over medium heat. Add salsa and simmer until slightly thickened and reduced to 4 cups, about 10 minutes. Stir in salt.

PICKLED RED ONIONS:

Toss first 3 ingredients in large glass bowl. Add juice and vinegar; press down to submerge onions. Cut 1/2 inch long slit in narrow tip of chile and add to onion mixture. Top mixture with small plate to weigh down slightly. Cover, refrigerate overnight. Drain. (Can be made one week ahead, keep refrigerated).

ENCHILADAS:

Char chiles directly over gas flame or in broiler until blackened all over. Enclose in paper bag, let stand 10 minutes. peel and seed, then cut into 2 x 1/2 inch strips.

Preheat oven to 375 degrees. heat 2 tbsp oil in medium skillet over medium heat. Add 1 tortilla to skillet; cook until slightly softened, about 15 seconds per side, turning with tongs. Transfer tortilla to paper towel to drain. repeat with remaining tortillas, adding oil to skillet as needed.

Spread 1/2 cup salsa over bottom of 8 x 8 x 2" glass baking dish. Arrange 4 tortillas over salsa, covering bottom of dish completely, overlapping slightly, and extending about 1.5" up sides of dish. Scatter 1 cup chicken over tortillas, then half of poblano strips. Spoon 1.5 cups salsa over, spreading evenly. Spoon 1/4 cup sour cream over in small dollops. Cover with 4 tortillas, overlapping slightly. Layer with remaining 1 cup chicken, remaining poblanos, 1 cup salsa and 1/4 cup sour cream. Cover with remaining 4 tortillas, then 1 cup salsa and remaining 1/4 cup sour cream. Sprinkle with cheese.

Bake casserole until bubbling and cheese is lightly browned, about 35 minutes. Cut into 6 pieces; divide among plates. Sprinkle with cilantro. Spoon pickled red onions alongside; serve.