Heat the oven to 350 F.
Put the butter in a 13x9-inch baking pan; put in the oven to melt.
In a shallow bowl, combine the egg, water, and lemon juice; blend well.
In another shallow bowl, combine the flour, salt, pepper, and onion powder.
In another shallow bowl, put the crumbs.
Coat each tilapia fillet with the flour mixture, dip in the egg mixture, then coat with the crumbs. Arrange the coated fillets on the baking sheet; turning to coat lightly with the butter.
Bake for 12 to 16 minutes, or until fish flakes easily with a fork.
Calories per serving: 344