BROWN meat in medium nonstick skillet on medium heat. Add dressing and chili powder; mix well. Cook 2 minutes, stirring occasionally. Reduce heat to low.
ADD beans and corn; mix well. Simmer 2 minutes or until heated through. Remove from heat. Add peppers and tomato; mix lightly.
SPOON evenly into taco shells. Top each with 1 Tbsp. of the sour cream.