Preheat oven to 350 degrees. Grease a 9x9 or 8x8 inch baking dish, or cast iron skillet and set aside.
Add the quartered strawberries to a large bowl then add in the sugar, cornstarch, lemon juice, and vanilla extract. Stir to combine and pour into prepared baking dish.
FOR THE TOPPING:
In a medium bowl use a fork to stir together the oats, flour, both sugars, lemon juice, lemon zest and melted butter until well combined and crumbly.
Evenly sprinkle the mixture over the strawberry filling.
Bake in preheated oven for 30-40 minutes until hot and bubbly.
NOTE ON PAN SIZE: You don't have to use a cast iron pan for this recipe. Any type of 9x9 or 8x8 baking dish will do. Note that you can also double or even triple this recipe and use a 9x13 inch baking dish as well.