Prep the chicken: Slice the chicken breasts in half horizontally to create thin cutlets. Pat dry and season on both sides with salt, pepper, garlic powder, and Italian seasoning.
Brown the chicken: Heat olive oil in a large skillet over medium-high heat.
Sear the chicken 3–4 minutes per side until golden and cooked through. Remove to a plate and tent with foil.
Sauté aromatics: Lower heat to medium. Add a small splash of oil if needed, then sauté the minced garlic for 30 seconds until fragrant.
Stir in the sun-dried tomatoes for another 30–60 seconds.
Build the sauce base: Stir in chicken broth and Dijon. Scrape up any browned bits on the bottom of the pan—they add flavor.
Make it creamy (light): In a small bowl, whisk milk and Greek yogurt until smooth. For a thicker sauce, whisk cornstarch into the milk before adding the yogurt.
Turn heat to low and slowly stir the mixture into the skillet.
Melt and season: Stir in Parmesan until melted. Add a pinch of red pepper flakes if you like a little heat. Taste and adjust salt and pepper.
Add greens: Fold in spinach and cook 1–2 minutes until wilted.
If using kale, simmer until tender, 3–4 minutes.
Finish the chicken: Return chicken and any juices to the pan, spoon sauce over the top, and warm for 1–2 minutes. If the sauce gets too thick, loosen with a splash of broth.
Serve: Garnish with fresh basil or parsley and a squeeze of lemon. Pair with zucchini noodles, steamed veggies, roasted potatoes, or whole-grain pasta.