Preheat your oven to 375F and move the rack to the middle position.
Sprinkle the chicken thighs with salt & pepper and the garlic powder (both sides), then coat them in flour and shake off any excess.
Heat the olive oil and butter in a skillet over medium-high heat for a few minutes. Once the pan is hot, sear the chicken for 6-8 minutes skin side down or until it's nicely browned, then cook the other side for 3-4 minutes. Transfer the chicken to a plate.
Add the mushrooms, onions, and Italian seasoning to the skillet. Sauté for about 6-8 minutes, stirring occasionally. The mushrooms should get a nice sear and release all their water (let the water cook off).
Stir in the garlic and Dijon mustard and cook for about 30 seconds.
Add in the wine and chicken broth. Give it a good stir and scrape up any brown bits from the bottom of the pan. Bring it to a bubble, then add the chicken back into the pan (skin side up).
Transfer the skillet to the oven and cook for 20 minutes.
Sprinkle with the fresh parsley and season with extra salt & pepper if needed.