Season the Chicken: In a large bowl, coat the chicken pieces with kosher salt, smoked paprika, and Montreal chicken seasoning. Let sit for 10-15 minutes to allow the flavors to infuse.
Sear the Chicken: Heat a large skillet over medium-high heat. Melt the butter and sear the chicken pieces for about 4-5 minutes per side until golden brown. Remove the chicken from the skillet and set aside.
Sauté the Aromatics: In the same skillet, add the minced red onion and cook until softened. Stir in the garlic, red pepper flakes, and half of the parsley, cooking for another minute until fragrant.
Simmer in Flavor: Pour in the chicken stock and lemon juice, scraping up any browned bits from the bottom of the skillet. Return the chicken to the pan, cover, and simmer over low heat for 20-25 minutes until the chicken is fully cooked.
Make it Creamy: Stir in the heavy whipping cream and Parmesan cheese, letting the sauce thicken for about 3-5 minutes.
Garnish and Serve: Sprinkle with the remaining parsley, then serve hot with your favorite side dish like mashed potatoes, rice, or roasted vegetables.