Line an 8 or 9-inch pan with parchment paper, leaving overhang for easy removal
Mix oats, rice cereal, and flaxseed in a large bowl
In a microwave-safe bowl, combine butter, honey, and brown sugar
Microwave for 1 minute, stir, then microwave for 1½ more minutes
Stir in vanilla extract
Pour syrup over dry ingredients, mixing gently to coat
Fold in chocolate chips
Press mixture firmly into prepared pan
Refrigerate for 1-2 hours before cutting