Place Chex cereal in large bowl.
In microwave, melt white chocolate chips and butter until melted, stirring every 30 seconds.
Add lemon juice and zest; quickly stir to combine.
Pour over cereal and coat well.
Toss powdered sugar into large brown paper bag or large bowl. Mix or shake in bag until coated.
Spread on baking sheets to dry, about 1 hour.