Place the mango and icing sugar in a bowl and toss to coat. On one side of each bread slice, create a pocket to stuff the mango into by using a sharp paring or serrated knife to carefully cut and create a deep - about 4” long - slit into the bread. Slide 2 to 3 mango slices into the slit in each bread slice, and then set bread on a baking sheet.
Combine eggs, milk, juice and spices in a large bowl. Preheat your electric griddle to, or set a large skillet over, medium to medium-high heat, melt and spread butter on the cooking surface. Dip the bread slices in the egg mixture. Cook the dipped bread slices, in batches if needed, 3 to 4 minutes per side, or until golden brown, and then divide among plates.