Preheat oven to 350°F. Spray a 9x13-inch baking pan with nonstick spray and set aside.

In a large bowl, stir together the diced strawberries and sugar. Let sit for 10 minutes. After 10 minutes, add lemon juice and cornstarch and stir to combine.

In the bowl of a stand mixer, mix oats, flour, sugar, cinnamon, butter, salt, and vanilla on low speed until the butter is evenly dispersed and the mixture resembles coarse meal.

Using your hands or the bottom of a measuring cup or glass, firmly press 2/3 of the crust mixture into the bottom of the prepared pan. Spread the strawberry filling evenly over the top of the crust.

Sprinkle the remaining crust mixture over the top of the strawberry filling, squeezing together some of the mixture into clumps to create a crumb-like topping.

Bake bars for 35-40 minutes or until golden brown. Allow to cool completely before cutting.