Pat the chicken dry. Season both sides with seasoning salt or salt and black pepper, garlic powder, and cracked black pepper.
Heat olive oil in a large skillet over medium-high heat. Add the chicken and cook for about 5–6 minutes per side, until golden and cooked through with an internal temperature of 165°F. Remove chicken from the skillet and set aside.
Lower heat to medium. Add butter to the same skillet. Once melted, sauté garlic for 1 minute.
Whisk in flour, and cook 1 minute.
Pour in chicken broth (and white wine if using), scraping up all the browned bits from the pan.
Stir in Dijon mustard, onion powder, and additional cracked peppercorns. Let it simmer for 3–4 minutes to reduce slightly.
Pour in heavy cream and stir well. Let the sauce simmer another 3–5 minutes until it thickens.
Return the chicken to the skillet, spooning the sauce over the top. Let it simmer for 2–3 minutes.
Garnish with parsley if desired. Serve as is or over rice, mashed potatoes, or rice.