Preheat your oven to 375°F (190°C) and line a muffin tin with paper liners.
In a large bowl, whisk together the flour, baking powder, baking soda, salt, and granulated sugar.
In another bowl, mix together the egg, buttermilk, orange juice, and melted butter until well combined.
Pour the wet ingredients into the dry ingredients and gently fold until just combined. Do not overmix.
Carefully fold in the cranberries until evenly dispersed in the batter.
In a separate bowl, combine the brown sugar, oats, cinnamon, orange zest, and melted butter for the streusel topping.
Scoop the muffin batter into the prepared muffin tin, filling each liner about 2/3 full.
Sprinkle the streusel topping generously over each muffin.
Bake the muffins for 18-20 minutes, or until a toothpick inserted into the center comes out clean.
Allow the muffins to cool in the tin for 5 minutes before transferring to a wire rack.
Serve warm or at room temperature, enjoying the burst of flavor in each bite!