Preheat the oven to 350°.
Place the chopped rhubarb and strawberries in a large bowl, and sprinkle with sugar, cornstarch, and almond extract.
Stir to combine, and let sit while you make the topping.
Cut the stick of butter up into tablespoon-size pieces or smaller.
Put the flour, butter, pecans, oats, salt, cinnamon, and brown sugar into a medium bowl. Use a pastry blender or your hands to thoroughly mix everything together.
Spread the rhubarb mixture evenly in a 9 x 13 dish.
Sprinkle the topping over the rhubarb mixture, so it is evenly distributed.
Bake for 35-40 minutes. The filling will be bubbling at the edges, and the topping should be golden brown.
Serve warm with ice cream or whipped cream.