Mix butter & brown sugar in a stand mixer. Scrape bowl. Combine dry ingredients & mix with butter/sugar mixture until combined.

Lightly spray a 9x13" pan. Press ¾ of the crumb mixture into the bottom. Set the rest of the mixture aside.

In a separate bowl, combine condensed milk, lemon zest, & lemon juice. Whisk until thickened. (If you do the homemade version like I did, just pulse the zest & juice in your blender after you have made the sweetened condensed milk.)

In a small food processor, blend whole strawberries with 1 Tbsp sugar (or more depending on the tartness of the berries.) Add water 1 Tbsp at a time until you have a thick, but pourable texture. (I actually used freeze dried strawberries, reconstituted them, & then pureed them in the food processor. I probably needed way more water than you would if you use fresh, so I won't guess the amount you would need for fresh berries; just don't water it down too much.)

Pour lemon mixture over prepared crust. Using a spoon dollop strawberry mixture on top of the lemon mixture & then swirl the mixture together to create a marbled look.

Sprinkle the remaining crumb mixture over the top.