Heat oven to 350ºF. Line twelve medium muffin cups with paper baking cups or spray bottoms only with cooking spray. For streusel, combine all ingredients in medium bowl; mix well. Set aside. For muffins, combine flour, oats, chocolate chips, baking powder, baking soda and salt in large bowl; mix well. In medium bowl, combine buttermilk, honey, oil and egg; blend well. Add to dry ingredients all at once; stir just until dry ingredients are moistened. (Do not overmix.) Fill muffin cups almost full. Sprinkle with reserved streusel, patting gently. Bake 20 to 22 minutes or until light golden brown. Cool muffins in pan on wire rack 5 minutes. Remove from pan. Serve warm.