Preheat the oven to 350°F (175°C).
In a large mixing bowl, combine the sliced strawberries, chopped rhubarb, granulated sugar, ¼ cup flour, and vanilla extract. Mix well until the fruit is evenly coated.
Transfer the fruit mixture into the greased baking dish, spreading it evenly.
In another bowl, prepare the topping by combining the rolled oats, brown sugar, ½ cup flour, melted butter, and ground cinnamon. Stir until crumbly and well mixed.
Sprinkle the oat topping evenly over the fruit mixture in the baking dish.
Bake in the preheated oven for about 40 minutes, or until the topping is golden brown and the fruit is bubbly.
Remove from the oven and let cool for a few minutes before serving.
Serve warm with a scoop of vanilla ice cream for an extra treat.