Mix together the flour, baking powder, baking soda, sea salt, and oats in a medium bowl until well-combined. Set aside.
Beat the butter, granulated sugar, brown sugar, orange zest, and vanilla together until light and fluffy - about 3 - 5 minutes on a stand mixer.
Add the egg to the butter mixture and beat for about an additional 2 - 3 minutes.
Pour the flour and oat mixture in with the butter mixture and stir until just combined.
Fold in the cranberries.
Cover the dough and chill for about 30 minutes, up to overnight.
Line two baking sheets with silicon baking mats or parchment paper. Preheat the oven to 350°F.
Portion out the dough into balls roughly 1 ½ - 2 tablespoons big. (If you chill overnight, you will need to allow the dough to rest at room temperature for about 5 - 10 minutes after portioning them out.) Place them on your baking sheets.
Bake for about 12 - 15 minutes, or until the edges are a light golden brown.
Allow the cookies to rest on the baking sheets for about 5 minutes before transferring to wire racks to cool completely.
Once cooled, melt your white chocolate and drizzle over the cookies.
Store cookies in an airtight container for up to two weeks. Store unbaked cookies in an airtight container in the freezer for up to a month, thaw in refrigerator before baking.