In a large skillet, heat olive oil over medium heat. Add sliced onion, allow to brown and season with salt.

In another skillet, heat olive oil over medium heat. Add mushrooms, salt and let it cook. 

Heat some oil in a saucepan, add tomatoes cut in half and grated, ground black pepper, salt, ground ginger, ground red pepper, cover and leave for 15 minutes. 

Preheat oven to 220°C (425°F).

Remove leaves from the cauliflower and cut it into florets.

Add the cauliflower florets into a food processor and pulse until it ressembles rice.

Line a baking sheet with parchment paper, add the cauliflower rice and bake in the preheated oven for 20 minutes.

Let the cauliflower cool then transfer it to a clean kitchen towel and squeeze out the excess moisture as hard as you can.

In a large bowl, combine cauliflower, beaten egg, grated cheese, salt, gound black pepper and dried thyme.

Line a baking sheet with parchment paper, place dough in the middle and use your hands to form a 1/4 inch thick circle.

Bake for 25 minutes until golden.

Top with onions, tomato sauce, tuna, mushrooms and cheese. Bake again for another 10 minutes.