Cream butter; gradually add 1/4 cup sugar, beating until light and fluffy. Stir in lemon rind. Add egg yolks, one at a time, beating well after each addition.
Drain apricot halves, reserving 1 tablespoon syrup; set apricots aside. Add reserved apricot syrup to batter, stirring well.
Combine flour and baking powder; add to batter, beating well. Spoon filling into tart shells. Bake at 375° for 20 minutes or until lightly browned.
Place one apricot half on each tart. Beat egg whites (at room temperature) until foamy. Gradually add remaining sugar, 1 tablespoon at a time, beating until stiff peaks form and sugar dissolves. Spread meringue over apricots, sealing to edge of pastry. Bake at 350° for 8 minutes or until meringue is golden brown.