Break apart the tofu block into 4 pieces and add into food processor. Process the tofu until smooth and creamy. If it doesn't get creamy, add a tiny splash of almond milk to help it along.
In a skillet, sauté the leek (or onion) and garlic over medium heat for a few minutes. Add a little broth if it starts to stick. Stir in the mushrooms and tomatoes, season with salt, and cook on medium-high heat until most of the water cooks off the mushrooms, about 10-12 minutes.
Stir in the herbs, spinach, nutritional yeast, sea salt, cayenne, black salt, and pepper until combined. Cook until the spinach is wilted.
Remove from heat and stir in the creamy tofu until thoroughly combined. Adjust seasoning to taste if desired. Spoon mixture into baked crust and smooth out with a spoon until even.
Bake quiche, uncovered, at 375F for 30 minutes, until the quiche is firm to the touch. For best results, cool the quiche for 20 minutes on a cooling rack before attempting to slice.
Notes
Wrap up leftovers and refrigerate for 3-4 days. Leftover quiche can be reheated in the oven on a baking sheet for about 15-20 minutes at 350F.