Cream margarine, 1 cup granulated sugar and brown sugar in large bowl. Add eggs, 1 at a time, beating well after each addition. Add vanilla. Beat.
Combine next 4 ingredients in small bowl. Add to margarine mixture. Stir until just moistened.
Add rolled oats and chocolate bar pieces. Stir well. Roll into 2 inch balls. Arrange 4 to 6 balls, about 4 inches apart, on greased cookie sheet.
Dip flat bottomed glass into second amount of granulated sugar. Flatten cookies to 1/2 inch thickness, dipping glass in sugar as necessary. Baked in 375°F oven for about 11 minutes until golden. Let stand on cookie sheet for 5 minutes before removing to wire rack to cool. Repeat with remaining dough. Makes about 3 dozen cookies.
VARIATION: For smaller cookies, roll dough into 1 1/2 inch balls. Arrange balls, about 2 inches apart, on greased cookie sheets. Flatten cookies slightly with flat bottomed glass dipped in second amount of granulated sugar. Bake in 375°F oven for 8 to 10 minutes until golden. Let stand on cookie sheets for 5 minutes before removing to wire racks to cool. Makes about 5 dozen cookies.