Arrange half the bread in the bottom of a greased 9-inch square baking pan. In a bowl, toss the bananas, coconut, and lemon juice; distribute evenly over the bread layer, and top with the remaining bread. In a bowl, beat the eggs and brown sugar. Beat in the half-and-half, milk, and vanilla to blend thoroughly. Pour over the bread, and press the bread down slightly to saturate it completely. Bake in a 400F oven until the bread is browned and the custard is set, 45-55 minutes. Cool slightly. Dust with powdered sugar, and garnish with additional banana slices. Serve warm. Top with whipped cream or vanilla ice cream, if desired.