Combine the cassava flour, baking soda, cream of tartar, salt, garlic powder, za’atar, crushed red pepper, and feta cheese powder in a large bowl.
In a separate bowl, beat the egg and add the water, gently combining the two.
Add the wet mixture to the dry ingredients and slowly whisk all ingredients together. If the mixture is too runny, add another 1-2 tablespoons of flour. If the mixture is too clumpy, add another 1/4th cup of water.
Allow the mixture to sit for about 20 minutes.
While the waffle batter is sitting, heat the olive oil in a pan over medium-high heat.
Add the coarsely chopped spinach and sauté until wilted. Remove from heat and allow to cool.
Once the spinach has cooled, fold it into the waffle batter.
Lightly spray your waffle maker with oil, and pour about 1/4th cup of batter per waffle.
Once the waffles are finished, top with crumbled feta cheese and tzatziki, and serve immediately for the perfect, crispy waffle!