Preheat your oven to 325°F and move an oven rack to the top third of your oven.
Pulse pecans, flax seeds, and half the oats in the bowl of your food processor or blender until coarse and equal in texture.
Combine remaining oats with pecan mixture in a large bowl.
Combine butter, maple syrup, and peanut butter in a microwave safe dish and heat in 30 second increments until melted. Stir to combine.
While rapidly whisking the egg whites, slowly drizzle in the warm melted peanut butter mixture. Continue to add it slowly until more than half is added. Continue to whisk and add the remaining liquid until completely combined.
Pour egg white and peanut butter mixture into the oat and pecan mixture. Fold until the oats and pecans are well moistened and peanut butter is well distributed.
Dump the granola bar mixture onto a baking sheet and shape into a large rectangle. Press to 1/4" thickness for crisp bars, up to 3/4" thick for soft chewy bars.
Bake the shaped bars in the top third of your oven for 16 minutes.
Allow to cool for at least 5 minutes, up to 10.
Use a butter knife to cut the granola bars into your desired shape and length. Spread them gently so there is at least 1/2" between each bar.
Return to the oven for 3 to 5 minutes, or until edges feel drier. Remove from oven and transfer to a cooling rack until completely cool, then store.
Notes
*please note that ounce measurements provided are by weight, not volume.*Use natural, unsweetened peanut butter to keep this recipe low sugar.*Only add salt if peanut butter and nuts are unsalted