In a medium sized bowl, whisk together the flours, salt, and gluten replacement or xanthan gum.
Next, cut in the butter substitute and crisco - be sure they are very cold! With the tips of your fingers, squish the flour into the fats until they have combined and look crumbly.
Add in the cold water and bring the dough together. Do not over mix.
Wrap the dough in saran and place in the fridge for 30 minutes while you prep the filling.
Heat the olive oil in frying pan over medium heat. When hot, add the onion and sauté for 5 minutes.
Add the diced mushrooms and continue to sauté for another 5 minutes, or until the mushrooms have cooked through and released their liquid.
Add the garlic, sun-dried tomatoes, and capers.
Add the spinach and cook until wilted. Turn off the heat and set aside until while you make your "egg." Keep the cheese for later, you'll mix it in at the end
Place all the ingredients into a blender and blend until smooth.
Preheat the oven to 375 degrees Fahrenheit.
Press the dough into a tart shell. It will be crumbly, but don't worry! It might take some time to spread it out evenly -- but it will come together! Poke a some holes in the bottom of the crust using a fork.
Take your "egg" mixture and add it to the sautéed veggies along with the shredded vegan cheese. Mix well.
Place the filling into the tart shell and spread the top so it's even (it won't spread perfectly and you don't want it to, anyways!)
Optional, but recommended: Spray the top of the tart with a little oil, or brush some olive oil on top.
Bake for 35 - 40 minutes.
Remove from the oven and let it cool for a couple minutes before cutting into it. Serve warm or cool. Once cool, I love wrapping up individual pieces and eating them as an on-the-go breakfast!