In a bowl, mix oats, flour, coconut, 1/4 cup sugar, and the salt. Add melted butter and stir until well blended. Press dough evenly into the bottom of a 9- by 13-inch baking pan.
Bake in a 325° oven until edges begin to brown, 15 to 18 minutes. Let cool about 5 minutes, then spread jam evenly over warm crust.
In a large bowl, with an electric mixer on high speed, beat egg whites and cream of tartar until thick and foamy. Gradually add remaining 2/3 cup sugar and continue to beat until mixture holds soft, shiny peaks. With a spatula, spread meringue evenly over jam.
Bake until meringue is lightly browned, about 20 minutes. Let cool 5 minutes, then cut into 24 bars. Let cool completely in pan.