Preheat oven to 375°F and lightly grease a 11-inch x 7-inch baking dish.
Heat the olive oil in a skillet over medium to medium-low heat. Add the chopped leeks and season with ¼ teaspoon salt. Saute until soft, about 3 minutes.
Add the garlic and cook for one more minute. Stir in the mushrooms, red bell pepper, and remaining ½ teaspoon salt and saute for several minutes until vegetables soften.
Add two handfuls of baby spinach to the skillet and stir to combine. Cook until the spinach is mostly wilted, about 3 minutes more, then turn off the heat. Stir the artichoke hearts into the mixture. Set aside.
In a large mixing bowl, whisk together the JUST Egg, soy milk, vegan Greek-style yogurt, Dijon mustard, ½ cup vegan Parmesan, vegan Cheddar, kala namak, garlic powder, and onion powder until thoroughly combined.
Pour the spinach and vegetable mixture into the prepared baking dish; then pour the JUST Egg mixture over it, gently combining with a spatula. Top with the remaining vegan Parmesan cheese and place the cherry tomato halves on top.
Bake until the edges are golden brown and crispy and the JUST egg is completely set in the middle, 65-70 minutes. If the edges brown too much during baking, cover with aluminum foil. Let cool for 10 minutes on the counter before serving.
Notes
Check if this vegan frittata is done by inserting a sharp knife into the center of the frittata - if it's liquid, place it back in the oven and keep checking it every five minutes until it's cooked.
Store the frittata in an airtight container in the fridge for 2-3 days. Enjoy the leftovers at room temperature or reheat until warmed through.