HEAT oven to 350ºF.
POUR boiling water over combined dates and nuts; let stand 10 min.
MIX next 4 ingredients. Drain dates and nuts, reserving liquid. Mix mayo, sugar, chocolate, vanilla and reserved liquid in large bowl. Add flour mixture; mix well. Stir in dates and nuts. Pour into 13x9-inch pan sprayed with cooking spray.
BAKE 35 min. or until toothpick inserted in center comes out clean. Cool completely.