Season steaks with 1/4 teaspoon of the salt and 1/8 teaspoon of the pepper. Heat 1 tablespoon of the butter and 1 tablespoon of the oil in large nonstick skillet over high heat. Add half of the steaks and sear until just cooked through, about 3 minutes per side. Transfer to plate and keep warm. Repeat with remaining steaks.
Heat remaining 2 tablespoons butter and 2 tablespoons oil in skillet over high heat. Add mushrooms and onion; sauté until golden, about 8 minutes. Add broth, any accumulated juices from the steaks, lemon juice, paprika, remaining 1/2 teaspoon salt and remaining 1/8 teaspoon pepper. Cook until sauce thickens slightly, about 3 minutes. Pour over steaks, sprinkle with parsley and serve hot.