Heat oven to 350 degrees F. Lightly grease an 8-by-4-inch or 9-by-5-inch loaf pan with cooking spray with flour (like Baker's Joy or Pam Baking Spray, or spray with regular cooking spray and lightly dust pan with flour).

In a medium bowl, whisk together flour, oats, baking powder and salt.

In a large bowl or bowl of a stand mixer, beat together butter and brown sugar until light and slightly fluffy. Add eggs and 1 teaspoon vanilla; stir to combine.

Add flour mixture to butter mixture; stir to combine. Gently fold in chopped plums and blackberries.

In a small bowl, beat together cream cheese, remaining 1 teaspoon vanilla and sugar. Fold into batter just a few times so there are streaks of cream cheese throughout.

Make the oat streusel: Add all ingredients except the powdered sugar to a small bowl and mix with fingers until a clumpy, cohesive, streusel-y mix forms.

Pour batter into prepared pan; top with a few pieces of chopped plums and blackberries, if desired. Top evenly with oat streusel.

Bake 1 hour (this could be less if you use a 9-by-5-inch pan) until a toothpick inserted in the center comes out clean. If the top is browning too quickly, cover with a tent of foil.

Cool bread 15 minutes in pan, then carefully remove and transfer to a cooling rack to cool completely. Dust with powdered sugar before serving, if desired.