Tomato Spinach Chicken Pasta

 oz (300g) chicken tenders or chicken breast cut into strips

unsalted butter

crushed red pepper flakes, optional

smoked paprika or more, to taste

Kosher salt and freshly ground black pepper,

Italian seasoning

garlic, minced

medium onion, chopped

roma tomatoes, roughly chopped

fresh spinach

pasta cooking water

chicken stock

 oz (220g) pene or spaghetti, uncooked