Preheat oven at 350°F Place an oven rack in the middle.
Cut the chicken and bell pepper in fine slices. Cut the onions in rings.
In a non stick skillet, roast the chicken in a little bit of oil until cooked through and golden. Set aside.
In the same skillet, cook the bell pepper and onion in a little bit of oil about 5 minutes. Set aside.
Brown the mushrooms at high heat. Set aside.
Put the tortillas on a working sheet. In the center, put salsa from top to bottom.
Then put the chicken, bell pepper, onions, mushrooms. Sprinkle with grated cheese. Flip the sides until both sides touch. Put wet toothpicks in the tortillas to keep them closed.
On a baking sheet, put the tortillas and put in over, on the middle rack. Cook about 20 minutes until cheese begins to melt and tortillas are a little bit golden.
Remove from the oven and remove the toothpicks. Sprinkle with cheese and put back in oven under the broil a few minutes until the cheese is golden.