Heat oven to 375°F. Lightly spoon flour into measuring cup; level off. In large bowl, combine all base ingredients; mix with fork until crumbly. Press mixture evenly in bottom of ungreased 13x9-inch pan.
In medium saucepan, combine 1/2 cup brown sugar and 1/2 cup margarine. Heat over medium heat, stirring occasionally, until mixture comes to a full boil. Remove from heat; stir in coconut and nuts. Spoon over base; spread evenly with fork.
Bake at 375°F. for 12 to 18 minutes or until topping is bubbly and edges of base are golden brown.
Remove pan from oven. Sprinkle with chocolate chips. Let stand 5 minutes to soften chips. With back of spoon, carefully spread chocolate evenly over bars. Cool 1 1/2 hours or until completely cooled. Cut into bars.