Lightly spray a 9 x 9" ceramic baking dish with cooking spray; place banana slices on the bottom of the baking dish and set aside.
Combine the strawberries and rhubarb in a large bowl. Add honey, sprinkle with cornstarch and toss until fruit is well coated and place in prepared baking dish over the bananas.
In a medium bowl, combine the oats, half of almonds, baking powder, cinnamon, and salt; stir together.
In a separate bowl, whisk together the remaining honey, milk, egg, and vanilla extract, then add to the oats.
Pour the oat mixture over the strawberries and rhubarb, making sure to distribute the mixture evenly.
Sprinkle the remaining almonds over the the top.
Bake the oatmeal for about 40 minutes, or until the top is golden brown and the oatmeal has set. Serve warm from the oven.