-Pitted and sliced, opt. Fresh basil or cilantro -Sprigs, optional In 10" skillet,over medium high heat,heat 1 tbsp. oil;add onion and chili powder;cook about 5 minutes,stirring frequently until onion is tender and well coated with chili powder.Remove from heat; let cool slightly.Spoon onion into large bowl;wipe out skillet.Add ground beef,bread crumbs,egg and salt to onion in bowl;using hands or wooden spoon,blend well.Shape mixture into 1" balls. To skillet,add remaining 2 tbsp. oil;heat over medium high heat.Add meatballs;cook about 12 minutes until well browned on all sides and cooked through.Stir in taco sauce and tomato;bring to boil.Reduce heat to low;simmer 5 minutes to blend flavors.To serve: Arrange bed of shredded lettuce over platter.Spoon meatball mixture over lettuce; sprinkle with cheese,if desired.Garnish with avocado slices and basil spring,if desired;serve with taco chips.Makes 4 servings.