Slice each chicken breast in half lengthwise to create four thin cutlets.
Season both sides with salt and black pepper, then lightly coat each piece with flour.
Heat the olive oil in a large skillet over medium-high heat.
Cook the chicken for 4–5 minutes per side until golden brown. Remove and set aside.
Melt the butter in the same skillet.
Add the sliced mushrooms and Italian seasoning. Cook until the mushrooms release their moisture and become beautifully browned.
Transfer the mushrooms to the same plate as the chicken.
Add the minced garlic, chicken broth, lemon juice, and Dijon mustard to the skillet. Stir until the mustard is fully dissolved and simmer for 3–4 minutes until reduced by half.
Pour in the heavy cream and stir until smooth.
Return the chicken and mushrooms to the skillet. Simmer for about 5 minutes until the Creamy Mushroom Chicken is fully cooked and the sauce has thickened.
Taste and season with additional salt and pepper if needed.
Serve immediately with your favorite side dishes.