Add chicken and 1/2 jar of salsa to a pressure cooker and cook for about 15 minutes. (you can also bake in the oven for about 30-45 minutes) Once chicken is nice and tender, shred chicken with forks.
In the mean time, saute mushrooms and spinach in butter. Combine shredded chicken and mushroom/ spinach mixture. Set aside and prepare your soup mixture.
Mix soup, sour cream and hot sauce. Lay out tortillas on a flat surface and spread a little soup mixture on each tortilla. Reserve enough of the mixture to spread on the inside of your baking dish, and on top of your rolled enchiladas.
Using some soup mixture, spread on the bottom and sides of baking dish ( I use and 8x13 glass dish) Spoon a good amount of chicken/spinach mixture on each tortilla and roll them up. You don't need to seal the ends. Place each roll in a single layer in dish until the whole dish is filled.
Spread the remaining soup mixture on the top and poor the remaining salsa on top as well. If you have any chicken mixuture left you can throw that on top too. Sprinkle cheese over the whole thing and bake at 350 for about 30 minutes or until hot and bubbly.
I usually serve this with mexican rice. It is very rich, but so delicious!