Preheat your oven to 400 degrees F.
Dice the onion. In a skillet, add olive oil and sauté diced onions over medium heat until fragrant and translucent.
Add in diced cremini mushrooms. Sprinkle in salt and continue to sauté until mushrooms start to release their juices.
Add in two handfuls of spinach and stir for a few moments until the spinach begins to wilt. Kill the heat.
Break up extra firm tofu into smaller pieces, and add to a food processor. Add in nutritional yeast, melted cashew butter, salt, and pepper, and blend until the mixture is crumbly.
Slowly mix in plant-based milk, adding only 1 tbsp at a time. Blend until the mixture turns into a very thick paste. Add more milk if needed.
In a separate bowl, combine tofu mixture with the sautéed vegetables, and Nuts For Cheese's chipotle cheddar cashew cheese. Mix well.
Add the mixture into the already-formed pie crust, and smooth evenly into the dish. Bake at 400 degrees F for 1 hour, or until top looks nicely golden.
Brush the quiche with melted cashew butter, and allow 10 minutes to cool and firm. Enjoy!