In the bowl of a stand mixer, combine the oats, ground flaxseed, chia seeds, cinnamon, salt, peanut butter, honey, and vanilla. Mix on low with the beater blade until well combined. Stop and scrape the sides of the bowl if necessary.
Stir in the trail mix.
Roll the mixture into small balls, about 1-2 tablespoons per ball. Place in an airtight container and keep refrigerated for up to 2 weeks.
Use your favorite trail mix. If you want the nuts to be smaller, you can chop the nuts in the trail mix before stirring the trail mix into the mixture. You can also freeze the energy balls for up to 3 months.