Preheat oven to 350º.
Cut horizontally through center of steak, cutting to, but not through, other side using a sharp knife; open flat as you would a book. Combine salt, pepper, and paprika, stirring well; rub surface of both sides of steak with salt mixture.
Heat a large Dutch oven over medium-high heat. Coat pan with cooking spray. Add onion and bell pepper; sauté 5 minutes or until tender. Add garlic; sauté 1 minute. Add spinach; sauté 30 seconds or until wilted.
Spread onion mixture over steak, leaving a 1/2-inch margin around outside edges; fold top over onion mixture, and secure with wooden picks.
Wipe pan with paper towels; place over medium-high heat. Recoat pan with cooking spray. Add steak to pan; cook 5 minutes. Add wine and broth to pan; bring to a simmer. Cover and bake at 350° for 45 minutes or until steak is tender. Remove steak from pan. Cover and keep warm.
Place pan over medium-high heat; bring to a boil. Cook until reduced to 1 cup (about 10 minutes). Thinly slice steak; serve with sauce. Sprinkle with oregano.