Season the chicken: Mix salt, pepper, and garlic powder. Sprinkle evenly over both sides of the chicken.
Sear for flavor: Heat olive oil in a large skillet over medium-high heat.
Add chicken and sear 3–4 minutes per side until golden. Transfer to a plate; it will finish cooking in the sauce.
Soften aromatics: Reduce heat to medium. Add onion and cook 3–4 minutes until translucent.
Stir in garlic, Italian seasoning, and red pepper flakes; cook 30 seconds until fragrant.
Deglaze: Pour in chicken broth and stir, scraping up brown bits. Whisk in Dijon mustard.
Build the creamy base: Add cream cheese and stir until smooth and melted. Lower the heat and whisk in Greek yogurt and milk.
Keep the sauce just below a simmer to prevent curdling.
Add the cheeses: Stir in 1/2 cup mozzarella and the Parmesan until melted and silky.
Fold in greens and artichokes: Add spinach and cook until wilted. Stir in chopped artichoke hearts. Taste and adjust salt and pepper.
Nestle the chicken: Return chicken and any juices to the skillet.
Spoon sauce over the top. Sprinkle the remaining 1/2 cup mozzarella over everything.
Finish gently: Cover and simmer on low 6–8 minutes, or until the chicken reaches 165°F in the thickest part. Squeeze in lemon juice for brightness.
Garnish and serve: Top with chopped parsley.
Serve with rice, cauliflower rice, whole-grain pasta, or crusty bread.