Cut filet mignon lengthwise in half, then crosswise into 1/4-inch thick strips.
Heat 1 teaspoon oil in large nonstick skillet over medium-high heat until hot. Add half of filet; stir-fry 1 to 2 minutes or until outside surface of beef is no longer pink. Remove from skillet. Repeat with 1 teaspoon oil and remaining beef. Remove from skillet; keep warm.
Heat remaining 4 teaspoons oil in same skillet over medium-high heat until hot. Add potatoes. Cook 7 to 8 minutes or until browned and crisp-tender, stirring occasionally. Carefully stir in salsa, red pepper and garlic salt. Reduce heat to medium-low. Cook, covered, 10 minutes, stirring occasionally. Return beef to skillet. Add corn; cook 2 minutes. Remove from heat.
Stir in avocado. Serve with sour cream and cilantro.