Preheat broiler. Lightly coat a 2-quart square baking dish with cooking spray; set aside. Line a 15x10x1-inch baking pan with foil. Place tomatillos in the baking pan. Broil 4 to 5 inches from the heat for 6 to 8 minutes or until softened and charred, turning occasionally. Set aside to cool slightly.

In a large skillet heat oil over medium heat. Add onion and poblano chile pepper; cook and stir for 4 to 5 minutes or until tender and onion starts to brown.

In a blender or food processor combine tomatillos, onion mixture, cilantro, sugar, cumin and salt. Cover and blend or process until smooth, stopping and scraping down sides as necessary.

Spread 3/4 cup of the tomatillo mixture in the prepared baking dish. Arrange six of the tortilla halves over the tomatillo mixture, overlapping slightly. Top with 1 cup of the chicken, 1/2 cup of the cheese, and half of the salsa, spreading evenly. Add six more tortilla halves and top with 1 cup chicken, 1/2 cup cheese, and half of the remaining tomatillo mixture, spreading evenly. Add six more tortilla halves, the remaining 1 cup chicken, and the remaining tomatillo mixture. Top with the remaining six tortilla halves and the remaining salsa, spreading to cover completely.

Cover the dish with plastic wrap and chill for at least 8 hours or up to 24 hours. Cover and chill the remaining 3/4 cup cheese until needed.

Preheat oven to 375 degrees F. Remove plastic wrap. Cover dish with foil and bake for 40 minutes. Remove foil then sprinkle with the remaining 3/4 cup cheese. Bake about 20 minutes more or until heated through. Let stand for 10 minutes before serving. If desired, garnish with chopped tomato, chopped onion, sliced jalapeno, sliced green onions, and/or snipped fresh cilantro.