Heat up a pan with half of the ghee over medium-high heat, add chicken thighs, season them with salt, pepper, garlic powder and onion powder, cook them for 3 minutes on each side and transfer to a bowl.
Heat up the same pan with the rest of the ghee over medium-high heat, add mushrooms, stir and cook for 5 minutes.
Add mustard and water and stir well.
Return chicken pieces to the pan, stir, cover and cook for 15 minutes.
Add tarragon, stir, cook for 5 minutes, divide between plates and serve.