Preheat oven to 350 degrees F (175 degrees C). Grease and flour 2 muffin tins.
Mix flour, oat bran, salt, baking soda, baking powder, and cinnamon in a large bowl; form a large well in the center of the mixture. Add zucchini, papaya, carrot, applesauce, honey, eggs, vanilla extract, lemon zest, and lemon juice to the well; stir to combine batter. Spoon batter into prepared muffin tins, filling each 2/3 full.
Bake in the preheated oven until a toothpick inserted in the center of a muffin comes out clean, 18 to 20 minutes. Allow muffins to cool in the tin for 5 minutes before transferring to a cooling rack.
