Add all purpose flour, whole wheat flour, oats, yeast, vital wheat gluten, salt, pumpkin seeds, cranberries, and orange zest to a large mixing bowl. Stir to combine all the ingredients.
Make a well in the middle of the mixture and pour in the orange juice and ¾ cup of lukewarm water. Mix until you don't see any more flour. If the mixture feels dry and crumbly, add a little more water (up to ¼ cup) until all the flour has been mixed in and you have a shaggy, sticky dough.
Cover the bowl with plastic wrap or a towel and let it sit undisturbed for 12-18 hours (I usually do this step overnight). Place the bowl in a warm place to help the dough rise.
Preheat the oven to 450 degrees.
Put the dutch oven (with lid on) into the oven to preheat for 30 minutes. While the pot is heating, uncover the dough. You'll know it's ready because the top of the dough will be covered with tiny air bubbles. Punch the dough down with your fist and fold the dough over itself four times. You might need a sprinkle of flour if it's too sticky. Cover the bowl again and let it rise for 30 minutes (while the pot is heating).
Carefully (wearing two oven mitts), remove the pot from the oven and remove the lid. For easy cleanup, line the pot with a piece of parchment paper. Sprinkle the wheat bran over the bottom of the pot.
Use a spatula to gently scoop the dough into the pot. You will immediately hear it start to sizzle, so quickly put the lid on and put the pot back into the oven.
Bake covered for 40 minutes. Remove the lid and let it bake for 5 more minutes or until the crust is golden brown. Take the pot out of the oven and carefully grab both sides of the parchment paper to lift the bread out of the pot. Transfer it to a wire rack and let it cool completely for one hour before slicing.