Preheat oven to 375°. Lightly, spray a 11-in. x 7-in. baking dish with cooking spray, set aside.
Flatten each chicken breast half to 1/2-in. thickness. Season chicken with salt and pepper.
Place flour, paprika and garlic powder in a resealable plastic bag; add chicken, a few pieces at a time. Seal and shake to coat.
In a large pan over med-high heat, add the butter and olive oil. Once pan is very hot, add the chicken (make sure to shake off excess flour!) and brown for 2 minutes on each both side. Transfer to the baking dish.
In the same skillet, add the rest of the butter and saute mushrooms for about 3 minutes.
Meanwhile, in a separate bowl combine the broth,sour cream, lemon juice, lemon zest, 2 Tbsp flour, salt and pepper, whisk to combine. Add the mixture to the saute pan with the mushrooms and stir to combine. Cook the mushroom mixture for 2-3 minutes or until the sauce thickens slightly.
Then add the mushroom mixture to the top of the chicken and bake, uncovered, at 375° for 20-30 minutes or until chicken is no longer pink. Serve with a little parsley and fresh cracked pepper on top.