Using a small sharp knife, cut a 3-inch pocket about 2 inches deep in the top-crust side of each bread slice, cutting to but not all the way through to the other side. Set aside.
For filling, in a medium mixing bowl beat cream cheese with an electric mixer on medium to high speed for 30 seconds. Add 2 tablespoons sugar and, if desired, the 1/4 teaspoon cardamom. Beat until smooth. Stir in mango. Divide cream cheese mixture evenly among bread slices, spooning it into the pocket of each bread slice. Place bread slices in a 2-quart rectangular baking dish; set aside.
In a medium bowl whisk together eggs, yogurt, milk, honey, and vanilla. Slowly pour the egg mixture over bread slices. Using the back of a wide spatula, press bread down lightly to soak with egg mixture. Cover and chill for 2 to 24 hours, turning bread slices over once or twice during chilling.
Preheat oven to 350 degrees F. Line a 15x10x1-inch baking pan with parchment paper. Place pistachio nuts in a shallow dish. Dip the bread in the chopped pistachio nuts, turning to coat and pressing lightly to help the nuts stick.
Arrange bread slices in prepared baking pan. Bake, uncovered, for 30 to 35 minutes or until lightly browned and heated through, turning once halfway through baking. Serve with Mango Lassi Sauce or maple syrup.