Preheat oven to 200°C (392°F).
Combine buckwheat flour, salt, baking powder, sunflower oil (or other neutral oil) and water, in a medium-sized bowl. Stir to combine.
Line a baking sheet with parchment paper. Move the dough to a baking sheet and flatten the dough, using your hands.
Bake for about 5 minutes.
Make the pizza sauce. In a small bowl, add tomato sauce, tomato paste, garlic powder, coconut sugar, and oregano. Stir together.
Remove pizza from the oven. Evenly spread pizza sauce. Top with shredded cheese and sliced white button mushrooms.
Sprinkle some thyme and salt to taste.
Bake for 10-15 minutes.