Preheat oven to 350 degrees F (175 degrees C). Grease a baking dish with cooking spray.
Place chia seeds in a blender; grind into a meal. Mix in 1/2 cup plus 1 tablespoon water; let stand until thickened, about 5 minutes. Add agave nectar, sucanat, olive oil, and vanilla extract; blend until combined.
Mix walnuts, carob powder, brown rice flour, almond flour, baking powder, and salt together in a bowl. Pour in chia seed mixture; mix until batter is smooth.
Spread batter in the greased baking dish. Wet hands and pat down evenly.
Bake in the preheated oven until a toothpick inserted the center comes out clean, 40 to 45 minutes.