Quick Tri-Tip and Bell Pepper Fajita Sauté

In a small bowl, whisk sour cream and milk and set aside. In a large skillet, heat 2 tablespoons olive oil over medium-high heat. Season steak with oregano and salt and pepper. Cook 3 to 4 minutes per side for medium rare, or until an instant-read thermometer inserted into the thickest part registers 130 degrees F. Transfer steak to plate and let rest 5 minutes, then slice. Meanwhile, add remaining tablespoon oil to skillet. Add peppers and cook, tossing often, 6 to 8 minutes, until softened. Serve steak and peppers with tortillas, romaine, cilantro, and lime. Drizzle with sour cream mixture to garnish.