Cut the chicken into cubes and season with salt and pepper.
Heat olive oil in a pan until hot over medium-high heat. Add chicken to the pan and brown on each side.
Remove chicken from the pan and set aside on a plate.
Add mushrooms to the pan and cook until browned. Once browned, add onion and let cook until translucent.
Add chicken broth to the pan and allow to reduce slightly. About 3-4 minutes.
Add heavy cream, grain mustard, dried tarragon, and salt and pepper (to taste) to the pan. Mix together, then add the chicken to the pan. Let this reduce slightly. About 3-5 more minutes.
Serve up and enjoy a quick, easy, and delicious meal!