Preheat oven to 400°F. Line 36 1 3/4-inch muffin cups with paper bake cups or grease the cups; set aside. In a small bowl whisk together the flour, 1/2 cup brown sugar, baking powder, cinnamon, and salt; set aside.
In a medium bowl whisk together the buttermilk, egg, and melted butter. Stir the dry ingredients into the wet ingredients and stir until just combined. Fold in the apples. Set batter aside.
In a food processor combine the oats, pumpkin seeds, chilled butter, and 1 tablespoon brown sugar. Pulse to combine and chop the pumpkin seeds.
Spoon the batter into prepared muffin cups, filling each nearly full. Sprinkle each with about 1 teaspoon of the pumpkin seed mixture. Bake for 15 minutes or until lightly browned. Cool in cups for 5 minutes. Remove and cool completely.