Preheat oven to 375°F.
Pat chicken dry and season both sides with salt and pepper.
Heat olive oil in a skillet over medium-high heat and sear chicken 3–4 minutes per side. Transfer to a plate.
In the same skillet, sauté onion until soft. Add garlic and cook another 30 seconds.
Reduce heat and stir in cream cheese, sour cream, and mayo until smooth.
Add spinach, artichoke hearts, mozzarella, Parmesan, and red pepper flakes. Stir until fully combined.
Place seared chicken into a 9x13 baking dish. Spoon sauce over the top.
Bake for 20–25 minutes, or until chicken is cooked through and sauce is bubbly.
Let rest 5 minutes before serving.