Clean and cut the mushrooms into quarters.
Cut the chicken into cubes. Season and lightly oil the chicken pieces. Brown them in a hot pan with some olive oil and add the mushrooms at the end of cooking.
Mix the frozen pasta with the cold sauce and add the diced chicken and mushrooms.
Place in a gratin dish and cover with gratin cheese. Bake for 20 to 25 minutes at 180° C.
Replace the diced chicken with already roasted chicken to have less preparation, it also allows you to use the roast chicken not sold during the day.