Line a baking sheet with parchment paper. Place the frozen artichokes on the parchment paper, drizzle with just a bit of olive oil, season with salt to taste and roast for 35 to 40 minutes
While the artichokes are roasting, heat the oil in a non-toxic skillet over medium-heat; add the shallots and sauté for 3 to 4 minutes, or until shallots are soft. Season shallots with salt to taste.
Stir in the spinach and sauté until spinach just begins to wilt, about 30 seconds or so. Remove skillet from the heat and set shallot-spinach mixture aside.
Remove the artichokes from the oven, but keep the oven turned on and the temperature at 400 degrees.
Once the artichokes are cool enough to handle, use kitchen shears to cut them into bite-sized pieces. Add the cut artichokes and parsley into the skillet with the shallot-spinach mixture and gently toss ingredients together. Transfer the vegetable mixture to the pre-baked gluten free crust.
In a high speed blender, add the cashews, eggs, lemon juice, 1/8 teaspoon salt and 1 cup water. Process on high for at least one full minute, or until mixture is smooth and creamy. Pour the cashew-egg mixture into the mixing bowl with the vegetables. Top with sliced tomatoes and mushrooms.
Bake the quiche for 30 to 35 minutes or until the top is ever so slightly golden and the eggs are set. Let rest for at least 10 minutes before serving.