Preheat oven to 180 degrees C. Grease a 20x20cm pan. In a small saucepan, combine the dates, 1/4 cup brown sugar, orange zest, cloves, 1/2 teaspoon cinnamon, allspice, lemon juice and water. Cook over medium-high heat, stirring constantly, until dates are soft and the mixture becomes a thick paste, about 10 minutes. Remove from heat and set aside to cool.
To make the crust and topping stir together the oats, 1/2 cup brown sugar, flour, baking powder, bicarb soda, 1/2 teaspoon cinnamon and salt in a medium bowl. Cut in butter using a pastry cutter or your fingers. Mixture should be coarse and crumbly. Stir in 2 tablespoons water until evenly distributed.
Press about 2/3 of the crust mixture into the bottom of the prepared pan. Spread the date mixture evenly over the crust all the way to the edges. Sprinkle the remaining crust mixture over the date layer. Press down lightly.
Bake for 20 to 25 minutes in the preheated oven until the top is lightly toasted. Cool completely before cutting into bars.