Preheat oven to 350°F.
To make the crust, combine all-purpose flour and sea salt in a food processor. While the machine is running, slowly add cubes of cold vegan butter. Once a fine meal crumble is formed, slowly add the ice cold water. Stop the machine just as the dough comes together.
Place the dough onto a lightly floured surface and roll out until ¼” thick.
Cut out 5” wide circles. You should only need to roll out the dough twice and cut circles.
Gently press each circle of dough into the cups of a regular size muffin pan and bake for 10 minutes.
While the crust is baking, cook the shallots, mushrooms, and asparagus in olive oil over medium heat for 4 to 5 minutes. Add sea salt and ground black pepper to taste. Set aside.
Combine the remaining filling ingredients together in a high-powered blender until smooth. Pour this mixture into a large mixing bowl and fold in the cooked vegetables.
Fill baked crusts with the filling and bake for 20 minutes at 350°F.
While the quiche are baking, make the red pepper relish by sautéing red pepper and onion in olive oil over medium heat for 3 minutes. Add chilli flakes and garlic and cook for another 5 minutes. Bring heat to medium-low to prevent burning the garlic and onion. Add white wine vinegar, agave nectar, and dijon mustard, and simmer for 8 to 10 minutes until most of the liquid is absorbed.
Serve quiche right out of the oven with dollops of red pepper relish on top. Garnish with finely chopped chives if desired.