Preheat the oven to 350 degrees F (175 degrees C). Grease a 9x9-inch baking pan.

Mix oats, flour, brown sugar, cinnamon, and baking soda together in a medium bowl until combined. Stir in melted butter until evenly mixed. Remove 1 cup of the mixture and set aside. Pat remaining mixture into the bottom of the prepared pan.

Combine 1 cup reserved crumb mixture, raisins, marmalade, and pecans in a bowl. Sprinkle over the mixture in the pan.

Bake in the preheated oven until a toothpick inserted into the center comes out clean, about 30 minutes.

Meanwhile, combine powdered sugar, milk, butter, and cinnamon for icing in a bowl. Stir until well blended and smooth.

Remove bars from the oven and carefully cut into 3-inch squares while still warm, then cut diagonally to make a triangle. Drizzle with icing.