Place the chicken breasts in a stock pot along with 1 onion peeled and quartered. Add salt and cover with water then bring pot to boil. Reduce heat to low and simmer until chicken is cooked through, about 20 minutes. Remove chicken from the water and let cool slightly. Shred chicken with two forks and set aside.
Mince the remaining onion and toss together with the shredded chicken in a medium bowl; set aside.
Preheat oven to 350 degrees. Heat a large frying pan or non-stick griddle over medium-high heat and add canola oil. Carefully fry each tortilla one by one, about 2 minutes per side; set aside keeping warm in a towel until you've fried all 32 tortillas.
Spread 1 cup of the salsa verde in a thin layer on the bottom of a 9" x 13" baking dish. Pour 2 cups of the salsa verde in a shallow pie dish and, working one by one, carefully dip each tortilla in the salsa verde, coating each side. Scoop two rounded tablespoons of the chicken and onion mixture into each tortilla and roll tightly. Place in a large pan, seam side down, in a single layer. Drench entire pan with remaining 1 cup of salsa verde and sprinkle with crumbled queso fresco. Bake in oven for 15 minutes. Remove from oven and serve with sour cream, cilantro and/or additional queso fresco.