Preheat the oven to 375 degrees F, and butter the inside of a 9 x 13-inch baking dish.
In a large bowl, mix together the oats, 1/4 cup of the almonds, 1/4 cup of the optional coconut, baking powder, cinnamon, ginger, and salt.
In another bowl, whisk together the maple syrup, milk, egg, coconut oil or butter, and vanilla.
Sprinkle half of the rhubarb and strawberries over the bottom of the baking dish. (I use my hands to evenly distribute the fruit.) Cover the fruit with all of the dry oat mixture. Slowly drizzle the milk mixture over the oats. Scatter the remaining fruit, almonds, brown sugar, and coconut, if using, over the top.
Bake for 35 to 40 minutes or until the oat mixture has set. Remove from the oven and let cool for a few minutes.
This may be eaten immediately or made ahead and reheated or eaten cold. Store leftovers in the refrigerator. (I often prepare this the night before and like the way the flavors develop and the oatmeal sets as it sits overnight.)