Line a 9 x 9-inch baking pan with parchment paper.
In the bowl of a stand mixer, beat butter and sugar on medium-high until light and fluffy. Add vanilla and beat until incorporated.
Add flour and salt. Mix on low until dough comes together.
Press half the dough onto bottom of prepared pan, smoothing it until base is even. Set aside remaining half.
Slice guava paste 1/4-inch thick. Arrange guava slices in an even layer atop the dough.
Make streusel topping: To remaining dough, add oats, coconut, 2 tablespoons flour, and dark brown sugar. Mix to combine. Sprinkle topping evenly over guava slices.
Bake until top is golden, about 40 to 45 minutes. Once cool, remove from pan by lifting parchment and transfer to cutting board. Cut into squares.
