BEAT 1/2 cup margarine and sugar in large bowl with electric mixer on medium speed until light and fluffy. Blend in egg and vanilla. Add flour, 1/3 cup of the coconut and the salt; mix well. Cover and refrigerate 1 hour.
PREHEAT oven to 350°F. Shape dough into 36 balls, each about 1 inch in diameter. Roll in walnuts, then press walnuts gently into dough to secure. Place, 1 inch apart, on ungreased baking sheets. Press down centers with thumb.
BAKE 9 to 12 minutes or until lightly browned. Remove cookies from baking sheets; cool completely on wire racks. Place chocolate and 1 Tbsp. margarine in small saucepan; cook on medium-low heat until chocolate is completely melted and mixture is well blended, stirring frequently. Spoon 1/2 tsp. of the melted chocolate mixture into center of each cookie. Sprinkle evenly with remaining coconut. Store in airtight container at room temperature.