Preheat oven to 350 degrees F (175 degrees C). Grease the bottom only of a 9x5 inch loaf pan.
In a medium bowl, stir together the flour, rolled oats, nuts, baking powder and salt. Combine the pineapple, carrots, brown sugar, eggs, orange juice and oil in the blender. Blend at medium speed for about 30 seconds. Pour blended ingredients into the bowl with the dry ingredients, and mix until all of the dry ingredients are absorbed. Pour the mixture into the prepared pan.
Bake for 75 to 80 minutes in the preheated oven. Cool for 10 minutes before removing from the pan to cool completely on a wire rack. Cool completely before slicing and serving.