Heat oven to 350°F. Lightly spray 8- or 9-inch square metal baking pan with nonstick cooking spray. For topping, combine flour and brown sugar in small bowl; mix well. Cut in butter with two knives until mixture is crumbly. Stir in oats and chocolate chips. For cake, combine boiling water and oats in small bowl; set aside. In medium bowl, combine flour, baking soda and salt; mix well. In large bowl, beat sugars and oil with electric mixer until well blended. Add egg and vanilla; beat well. Add flour mixture and oat mixture; mix just until dry ingredients are moistened. (Do not overmix.) Stir in mini chocolate chips. Pour batter into pan. Sprinkle with reserved topping. Bake 50 to 60 minutes or until wooden pick inserted in center comes out with a few moist crumbs clinging to it. Cool in pan on wire rack. Store tightly covered at room temperature.