Prep the chicken: Slice large breasts in half horizontally to make thinner cutlets.
Pat dry and season both sides with salt and pepper.
Heat the skillet: Place a large skillet over medium-high heat. Add olive oil and 1 tablespoon butter and let it get hot and shimmering.
Sear the chicken: Add chicken in a single layer. Cook 4–5 minutes per side, until golden and just cooked through.
Transfer to a plate and tent loosely with foil.
Sauté aromatics: Lower heat to medium. Add remaining 1 tablespoon butter. Stir in minced garlic (and mushrooms if using).
Cook 30–60 seconds until fragrant, stirring so the garlic doesn’t brown.
Deglaze: Pour in chicken broth and scrape up browned bits from the pan. Let it simmer 2 minutes to reduce slightly.
Make it creamy: Stir in heavy cream, Italian seasoning, and a pinch of red pepper flakes. Simmer 3–4 minutes, stirring, until the sauce thickens enough to coat the back of a spoon.
Add parmesan: Reduce heat to low.
Sprinkle in parmesan a little at a time, stirring until smooth. If using spinach, stir it in now and let it wilt.
Finish the sauce: Add lemon juice and taste. Adjust salt and pepper as needed.
The lemon should brighten without making the sauce tangy.
Return the chicken: Add chicken and any juices back to the skillet. Spoon sauce over the pieces and simmer 1–2 minutes to warm through.
Garnish and serve: Top with chopped parsley or basil. Serve hot with zucchini noodles, cauliflower mash, or a simple green salad.