HEAT oven to 375°F.
MIX flour, baking soda and salt. Chop 2 oz. chocolate.
BEAT margarine, brown sugar and SPLENDA® 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.