I found this recipe from Two Peas and Their Pod. It was super easy and quite tasty! I had a hard time getting it out of the pan so the second time I made it I put some parchment paper on the bottom and everything went much better.
1 can Sweetened, Condensed Milk - 14-ounce Can
½ cups Lemon Juice
1-½ cup Flour
1 cup Oatmeal
1 cup Brown Sugar
⅔ cups Butter, Melted
1 teaspoon Baking Powder
1 pinch Salt
Preheat the oven to 350F.
Combine milk and lemon juice. Mix well and set aside for a moment.
Mix remaining ingredients until crumbly.
Press half of the streusel (dry) mixture into a lightly greased 9×13 baking dish. Pour the lemon mixture over top. Finish by sprinkling remaining streusel over the top of the lemon filling. Bake for 25-30 minutes. Cool completely then store in the refrigerator.