Season the chicken breasts with Italian seasoning, crushed red pepper, salt, and black pepper.
Heat olive oil in a large skillet over medium heat.
Add the chicken to the skillet and cook for 5–6 minutes per side until golden and cooked through. Remove the chicken and set aside.
Add 1 tablespoon butter, onion, and asparagus to the skillet. Cook for 2–3 minutes until the asparagus is tender-crisp.
Stir in the garlic and cook for about 30 seconds until fragrant.
Pour in the heavy cream and lemon juice, then stir in the Parmesan cheese if using.
Return the chicken to the skillet and let the Creamy Lemon Garlic Chicken with Asparagus simmer for 3–4 minutes until the sauce thickens.
Taste and adjust seasoning if needed. Add a splash of broth or water if the sauce becomes too thick.
Serve warm with rice, pasta, mashed potatoes, or roasted vegetables.