Preheat the oven to 375ºF (191ºC).
In a small bowl, combine the chia seeds and water. Stir and let sit for 5 minutes to form a gel.
In a mixing bowl, combine the strawberries or blueberries, rhubarb, and half of the date paste. Toss well, then spread evenly across the bottom of a silicone or parchment-lined square baking dish.
In another bowl, whisk together the almond milk, chia egg, and remaining date paste. Stir in the oats and cinnamon until well combined.
Pour the oat mixture evenly over the fruit. Sprinkle the chopped pecans and walnuts on top.
Bake for 40 minutes, or until the oats are set and the top is lightly golden. Let cool slightly before serving. Enjoy warm!