Place a steamer insert into a saucepan and fill with water to just below the bottom of the steamer. Bring water to a boil. Add pumpkin, cover, and steam until fully cooked, 35 to 45 minutes.
Preheat oven to 350 degrees F (175 degrees C). Grease a 9x5-inch loaf pan with olive oil.
Place chia seeds in a blender; add hot water and let sit for 5 minutes.
Scoop flesh out of pumpkin halves and add to blender. Add crystallized sugar cane juice and agave nectar to blender; blend until pumpkin mixture is very smooth.
Mix spelt flour, brown rice flour, baking powder, cinnamon, salt, nutmeg, allspice, and cloves together in a bowl. Fold pumpkin mixture and walnuts into flour mixture until batter is just mixed; spoon into the prepared loaf pan.
Bake in the preheated oven until a toothpick inserted in the center comes out clean, 1 to 1 1/2 hours.