Preheat the oven to 350°F (175°C). In a mixing bowl, combine the sliced strawberries, chopped rhubarb, granulated sugar, cornstarch, vanilla extract, and lemon juice. Toss until well combined.

Transfer the fruit mixture to a greased baking dish, spreading it evenly.

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

Sprinkle the crisp topping evenly over the fruit mixture in the baking dish.

Bake in the preheated oven for 30 minutes, or until the topping is golden brown and the filling is bubbling.

Remove from the oven and let cool for a few minutes before serving warm.