HEAT oven to 375°F.
MIX flour, baking soda and salt. Chop 2 oz. chocolate.
BEAT margarine, brown sugar and granulated sweetener in large bowl with mixer until light and fluffy. Blend in egg and vanilla. Gradually beat in flour mixture. Stir in chopped chocolate. Drop heaping tablespoonfuls of dough, 2 inches apart, onto baking sheets.
BAKE 11 to 12 min. or until lightly browned. Cool on baking sheets 1 min.; remove to wire racks. Cool completely.
MELT remaining chocolate as directed on package. Stir in COOL WHIP and water. Dip half of each cookie in chocolate; let stand until firm.