Preheat the oven to 350 degrees F (175 degrees C).
Stir rhubarb, strawberries, cornstarch, lemon juice, and honey together in a medium bowl; transfer to a shallow baking dish. Stir oats, brown sugar, and cinnamon together in the same bowl. Mix in butter with a pastry blender until crumbly; spread on top of fruit.
Bake in the preheated oven, until rhubarb is tender and the topping is toasted, about 40 minutes. Serve warm.
