In saucepan, bring dates, raisins, sugar, orange rind and juice and 1 ½ cups water to boil, stirring. Reduce heat and simmer, stirring often, until mixture is thick enough to mound on spoon, about 10 minutes. Stir in lemon juice; let cool.
Meanwhile, in large bowl, whisk together flour, baking soda and salt. Add rolled oats and brown sugar; blend evenly. Combine melted butter and vanilla; drizzle over oats mixture. Toss to moisten dry ingredients evenly.
Press half of the rolled oats mixture into greased 9-inch square metal cake pan. Evenly spread date filling over base. Sprinkle with remaining crumbs; press lightly.
Bake in centre of 350°F oven until topping is golden brown and firm, about 40 minutes. Let cool on rack. Cut into 16 squares. (Make-ahead: Layer squares between waxed paper in airtight container and store at room temperature for up to 3 days or freeze for up to 2 weeks.)