Preheat oven to 180C. Start by making your base by stirring together all ingredients until well combined and sticky. Press into the base of a spring-formed tart tin, then prick all over with a fork. Place in the oven to bake for 12-14 minutes, or until lightly golden. Remove and allow to cool.
Place tofu into a blender and blitz, adding milk one tablespoon at a time until the mixture is smooth but not runny - only add as much milk as you need to get the tofu lump-free, the mixture should be thick! This should be no more than 6 tbsp. Set aside.
Gently heat some olive oil in a pan. Fry the onion for a few minutes, then add in the garlic and cook until golden. Stir in the spinach, basil, Nutritional yeast, oregano and chilli flakes and cook until spinach has wilted.
Stir in the smooth tofu, then season well with salt and pepper to taste. Heat until warm. Remove from the heat.
Spoon the tofu mixture over the tart base, using the spoon to smooth the top. Press the tomato halves into the quiche, then place in the oven to bake for around 30 minutes, or until the quiche is firm to touch. Allow to stand for 5 minutes - or until cool - before cutting and serving.