Start by cutting the chicken breasts in half lengthwise to make thinner cutlets. This lets them cook evenly without drying out. Season both sides with salt and pepper, then lightly dredge in flour for a golden crust.
Heat olive oil in a large skillet over medium-high heat. Add the chicken and cook for about 4–5 minutes per side until it turns golden brown. Once done, transfer the chicken to a plate.
Add butter to the same skillet. Once melted, toss in the sliced mushrooms and Italian seasoning. Cook the mushrooms until they release their water and begin to gain a beautiful sear. Remove them from the pan.
Into the skillet, add minced garlic, chicken broth, lemon juice, and Dijon mustard. Stir well and allow the mixture to reduce by half, which takes about 3–4 minutes.
Lower the heat and add the heavy cream to the reduced sauce. Stir to combine before returning the mushrooms and chicken to the skillet. Cook for another 5–6 minutes, ensuring the chicken is fully cooked and its internal temperature reaches 165°F. The sauce will thicken slightly, and the dish will be ready to serve.