Preheat an oven to 400 degrees F (200 degrees C). Grease 12 muffin cups or line with paper muffin liners.
Stir the oats, flour, 1/4 cup sugar, baking powder, and raisins together in a bowl; set aside. Beat the egg in a bowl along with the orange zest and canola oil. Whisk in the milk and stir in the flour until just mixed. Evenly divide the batter among the prepared muffin cups.
Bake in the preheated oven until a toothpick inserted into the center comes out clean, about 20 minutes. Remove the muffins from the oven. Stir the orange juice together with 1 tablespoon sugar until the sugar dissolves. Drizzle 1 teaspoon of this mixture over each muffin, remove from the muffin tin, and allow to cool slightly before serving.
