In a large bowl, combine the strawberries, rhubarb, granulated sugar, cornstarch, vanilla extract, lemon juice, and ground cinnamon. Mix well and pour the mixture into the crockpot.
In a separate bowl, mix the rolled oats, all-purpose flour, brown sugar, melted butter, and salt until crumbly. Sprinkle this mixture evenly over the fruit in the crockpot.
Cover the crockpot and cook on low for 4-5 hours or until the fruit is bubbly and the topping is golden brown.
Once cooked, remove the lid and let it cool for about 10 minutes before serving.