Preheat your oven to 400° degrees and spray a 9 x 13 baking dish with non-stick spray. Set aside.
Trim your chicken breasts and then butterfly/cut them in half. Sprinkle with salt & pepper and lay them into the prepared dish.
In a large skillet, over medium heat, melt the butter.
Add in the chopped onion and saute until translucent.
Add in the minced garlic and cook for about 30 seconds.
Add in the cream cheese, Greek yogurt, and a pinch of salt & pepper. Stir and melt until fully incorporated.
Remove the pan from the heat and stir in the spinach, artichokes, half of the parmesan cheese and half of the mozzarella cheese until fully combined.
Spread the mixture evenly over the chicken. Cover the pan with foil and bake for 20 minutes.
After 20 minutes, remove the foil, add the rest of the parmesan & mozzarella cheeses and bake for another 10 minutes until the mixture is melted and bubbly.
Remove from the oven and let set for 10 minutes before serving.
Alternatively, you can use fresh baby spinach in place of the frozen spinach. Add it after sauteing the onion and garlic and heat until wilted, then proceed with the rest of the recipe as written.Store leftovers in the fridge, covered, for up to four days.If freezing, it is best to assemble and freeze before baking, for up to 3 months. Move the fridge the night before you're ready to serve to thaw and then bake as written.