For the poached chicken: Add 8 cups water, the chicken, salt and bay leaf to a large saucepan and bring to a boil. Reduce the heat to low, cover and cook for 10 to 12 minutes. Remove the chicken from the water and let sit until cool enough to handle. Shred or slice the chicken thinly and set aside.
For the green sauce: Preheat the oven to 450 degrees F.
Place the tomatillos, cilantro sprigs, jalapenos, garlic, lime and white onions on a baking sheet and roast until the tomatillos pierce easily with a fork, 15 to 20 minutes. Transfer the roasted ingredients, except for the lime, to a blender. Squeeze the juice from the roasted lime into the blender and discard the rinds. Add the coriander, cumin, salt and sugar and blend until the sauce is smooth. If the sauce is too thick, add 1/2 cup of water at a time until the desired consistency is reached. Set aside.
Reduce the oven temperature to 375 degrees F.
For the enchiladas: To assemble, pour 1 cup of the green sauce on the bottom of a 9-by-13-inch baking dish.
On a work surface, fill a tortilla with some of the poached chicken and about 2 tablespoons total of the Cheddar and Monterey Jack. Roll the tortilla like a cigar and lay in the baking dish seam-side down on top of the sauce. Continue filling and rolling the tortillas until the dish is full. Pour the remaining sauce on top of the rolled tortillas. Cover with the remaining shredded Cheddar and Monterey Jack and the queso fresco.
Bake until the cheese is bubbling and melted, 15 to 20 minutes. Garnish with scallions and radishes.