Preheat the oven to 325 degrees F (165 degrees C). Line two large baking sheets with parchment or aluminum foil.
Combine the oats, wheat germ, oat bran, almonds, pecans, and walnuts in a large bowl. Stir together the salt, brown sugar, maple syrup, honey, oil, cinnamon, and vanilla in a saucepan. Bring to a boil over medium heat, then pour over the dry ingredients, and stir to coat. Spread the mixture out evenly on the baking sheets.
Bake in the preheated oven until crispy and toasted, about 20 minutes. Stir once halfway through. Cool before storing in an airtight container.