Mix the cereal, graham crackers and chocolate chips in a large bowl. Grease or line with parchment and 9x13 pan. Heat the butter, marshmallows, true lime or lime juice and zest in a sauce pan over medium until melted and combined, stirring constantly. Add the vanilla.
Scrape this mixture into the bowl with the cereal and quickly mix well. Press into the 9x13 pan, using a greased hand to flatten it out. Allow to cool fully and cut into squares.