Preheat your oven to 375°F.

In a medium bowl, combine the oats, chia seeds (if using), and cinnamon.

Add the coconut oil or melted butter, apple purée, and egg (if using), and mix until well combined.

Line a baking tray with parchment paper.

Press the mixture into the bottom of the baking dish to form an even layer, about 1.5-2 cm thick.

Bake at 375°F for 25 minutes, or until the bars feel firm to the touch but not hard.