Cook meat and green onions in a large nonstick skillet over medium-high heat until browned, stirring to crumble. Drain well, and return meat mixture to pan. Stir in taco sauce, garlic powder, pepper, beans, and corn, and cook until thoroughly heated. Spoon 1 cup meat mixture over 1/2 cup chips, and top with 3/4 cup lettuce, 1/4 cup tomato, 1/4 cup cheese, 2 tablespoons salsa, and 2 tablespoons sour cream. Repeat with remaining ingredients.