Butterfly chicken breasts by slicing through one side of each breast almost all the way to the other side but not completely.
Mix together 2 tbsp of olive oil with the oregano, salt and pepper and use this mixture to season butterflied chicken breast by rubbing it all over them.
Place chicken breasts in butterfly position on a board or tray and set aside.
Heat 2 tbsp of olive oil in saute pan and add garlic saute until aroma releases.
Add spinach and saute until wilted, then remove from heat.
Tip spinach into a colander to allow excess water to drain away
Place one slice of provolone on top of each chicken breast
Divide spinach mixture into four portions then add a portion of spinach on top of the provolone on each chicken breast.
Fold chicken breasts to envelope the provolone and spinach then carefully place in a baking pan
Drizzle 1/3 of the tomato sauce over the top of the chicken breasts and brush over them evenly.
Place chicken breasts in a preheated oven at 425 and cook for 15-20 mins dependent upon thickness of chicken breasts.
Remove chicken from oven and place one breast on each plate or all four on a platter.
Pour the juices released from the baked chicken into the remainder of the tomato sauce and return to the heat.
Allow sauce to heat through and flavors combine, then pour over chicken and serve immediately.