Heat oven to 350°F.
Wrap tortillas in foil. Heat in 350°F oven for 10 minutes.
Puree avocado and lime juice in food processor. With motor running, add skim milk and buttermilk (see Note).
Transfer mixture to small bowl. Stir in cilantro, onion, salt and hot-pepper sauce. Cover surface directly with plastic wrap. Refrigerate until serving.
Place equal amounts of lettuce, chicken, red pepper and corn on each warmed tortilla. Top with guacamole dressing. Garnish with avocado slice, if desired. Serve immediately.