Slice the chicken breasts lengthwise to create four thinner cutlets. Season both sides with salt and black pepper, then lightly dredge in flour.
Heat olive oil in a large skillet over medium-high heat. Once hot, add the chicken cutlets.
Cook the chicken for about 4–5 minutes per side until golden brown. Remove from the pan and set aside.
Add butter to the skillet. Once melted, add the sliced mushrooms and Italian seasoning. Cook while stirring occasionally until the mushrooms release their moisture and develop a golden sear.
Remove the mushrooms from the pan and place them with the chicken.
Add minced garlic, chicken broth, lemon juice, and Dijon mustard to the skillet. Stir well until the mustard dissolves and allow the mixture to reduce by half, about 3–4 minutes.
Pour in the heavy cream and stir to combine. Return the chicken and mushrooms to the skillet.
Simmer for about 5 minutes until the chicken is fully cooked and the sauce thickens. This final step creates the rich flavor that makes creamy mushroom chicken so irresistible.
Taste and adjust seasoning with salt and pepper if needed before serving.