Season steak generously with salt and TABASCO® brand Chipotle Pepper Sauce; cover and refrigerate at least 30 minutes.
Wrap tortillas in foil and place in a 300°F oven for 15 minutes. Heat oil in a large skillet over medium heat and add onion and bell pepper; cook 3 to 4 minutes or until softened. Set aside and keep warm.
Grill steak over medium-high heat to desired doneness; cut into thin strips and toss with onions and peppers. Place 2 to 3 spoonfuls of mixture on each tortilla and top with avocado, sour cream and salsa.