Preheat oven to 425F
Clean and wash chicken as preferred
Lay each chicken breast on flat surface and slit horizontally making a pocket or butterfly, ensure not to cut all the way through. Around 3/4 of the way.
Combine seasonings in small bowl, add a drizzle of oil to chicken and season, set aside
Heat a large skillet and add 1 tbsp oil. Saute onions for 3 mins
Add garlic, saute for 2 mins, then add spinach. Cook together for around 5 mins
Add cooked spinach to a bowl along with remaining filling ingredients and mix well
Stuff each chicken breast with filling, ensuring not to over stuff.
Add butter to the same skillet and melt over medium high
Once melted, sear chicken pieces around 4-5 mins per side
Transfer to baking dish for and bake for 10-12 mins (depending on thickness)
Broil on low for 3 mins to get that extra seared look.