Preheat oven to 275 degrees F (135 degrees C). Grease a baking sheet.
Combine oats, wheat bran, coconut, raisins, almonds, sunflower seeds, pumpkin seeds, wheat germ, and flaxseed together in a bowl.
Mix honey, oil, brown sugar, and peanut butter together in a saucepan over low heat until dissolved, about 5 minutes. Whisk milk, vanilla extract, and baking soda together in a bowl; pour into honey mixture. Cook mixture, whisking constantly, until bubbling; remove from heat and immediately pour over dry ingredients.
Press oat mixture into the prepared baking sheet using your hands until top is smooth and mixture is evenly distributed.
Bake in the preheated oven until top is lightly browned, 20 to 25 minutes. Cool to room temperature and cut into bars.