Combine the ground flax seeds with water. Stir well and let it sit for about 3-5 minutes.
Meanwhile, combine the rest of the ingredients (except for the peanut butter and the peanuts) in a medium bowl. Stir gently with a wooden spoon until well combined.
Place baking cups in a muffin pan and divide the mixture evenly. Stir in some peanut butter and top each muffin with some peanuts.
Bake for about 15 minutes at 360°F (180°C). Let cool down in the muffin tin for at least half an hour.