You can divide the preparation of the vegan frittata by putting the chickpea batter alone in the fridge up to 12 hours, then add to it the cooked vegetables you prefer when ready to bake.
This vegan chickpea frittata can also be cooked in a pan. Use a non-stick type and lightly oil the bottom, heat it well then pour the chickpea batter and cooked vegetables. Be careful the pan is big enough to form a thin frittata (no more than half a centimeter thick). Cook over medium heat, 7 to 8 minutes per side until each is nicely browned.