Make the salsa: Put the tomatillos, jalapenos, and onion in a saucepan with the vinegar and water to cover. Bring to a boil, reduce the heat and poach until the tomatillos are soft, about 10 minutes. Drain. Put the vegetables in a blender, add the cumin, and puree. Add the cilantro, lime juice, and salt, and pulse to combine. Set aside.
Meanwhile, place the poblano peppers directly over the flame on a gas stove and cook, turning with tongs, until the skin is charred and blackened. (Or, if you have an electric stove, put the chiles on a baking sheet and broil, turning with tongs, until the skin is blackened.) Skin the peppers; then seed, core, and dice them.
Heat a 2-count of olive oil in a medium saucepan over medium heat. Add the onion and cook until softened and caramelized, 5 to 7 minutes. Add the garlic and cook 1 minute. Stir in the cumin and cook 1 minute. Then sprinkle on the flour and cook, stirring, 1 more minute. Gradually pour in the stock, stirring constantly. Bring to a simmer, stirring to make sure the flour doesn't stick to the bottom of the pan; the liquid will thicken. Fold in the chicken, diced peppers, and cilantro, and season well with salt and pepper.
To assemble the dish: Preheat the oven to 350 degrees F. Get your self a large baking dish. Dip a tortilla into the tomatilla salsa and put it on a cutting board. Put a big scoop of the chicken mixture in the center, sprinkle with a little of the cheese, and roll the tortilla like a cigar to enclose the filling. Use a spatula to place it seam side down in the baking dish. Continue to fill all of the tortillas and put them in the baking dish. Pour the remaining tomatilla salsa over the top and sprinkle with the remaining cheese. Bake uncovered for about 30 minutes until bubbly and cracked on top. Serve hot with the guacamole and sour cream.
Halve and pit the avocados. Scoop out the flesh with a tablespoon into a mixing bowl. Mash the avocados with a fork, leaving them somewhat chunky. Add the remaining ingredients, and fold everything together to gently mix. Lay a piece of plastic wrap right on the surface of the guacamole so it doesn't brown and refrigerate 1 hour before serving.