Coat an 8x8-inch baking pan with canola cooking spray. Put the butter, peanut butter, and marshmallows into a medium-sized microwave safe bowl and microwave on high for 30 seconds, or until mixture is just melted. Stir to blend.
Microwave again briefly if the mixture isn't melted or smooth. Then stir in granola, puffed rice and flaxseed.
Spread the mixture in the prepared pan, flattening it evenly with a sheet of waxed paper. Let it cool completely before cutting into 8 equal-sized bars.