Preheat the oven to 350°F (175°C). In a mixing bowl, combine sliced strawberries, chopped rhubarb, granulated sugar, flour, and vanilla extract. Mix well and set aside.

In another bowl, mix oats, flour, brown sugar, melted butter, and cinnamon until crumbly.

Spread the fruit mixture evenly in a baking dish. Sprinkle the oat topping over the fruit. Bake for 30 minutes or until the topping is golden brown and the fruit is bubbling.

Let cool slightly before serving. Enjoy warm, optionally with vanilla ice cream.