Pre-heat the oven to 200C/400F degrees.
Thoroughly grease a spring-form cake tin and line the bottom and sides with parchment paper.
Heat one tablespoon of the olive oil in a frying pan on a medium heat.
Add the red onion rings and gently cook until soft and tender.
Remove the onion from the frying pan. Set aside a few of the “good” onion rings as they will be placed on the top of the cake.
Rice the cauliflower by either grating it or running the florets in the food processor.
Place the cauliflower in the frying pan and cook for about 8-10 minutes, stirring occasionally.
In a large bowl, add the coconut flour, turmeric and baking powder. Stir to combine.
Add the cooked cauliflower rice, thyme, basil, Parmesan cheese, feta cheese, cooked onion and mustard. Mix thoroughly.
Add the beaten eggs, stir to combine and season with the salt and pepper.
Pour into the cake tin and place the reserved onion rings that you set aside on top of the cake.
Bake for 40 minutes until firm and golden brown.
Remove from the tin, eat and enjoy!