Preheat the oven to 400°F (205°C). Line the bottom of a 9-inch (23-cm) deep-dish pie pan or 10-inch (25-cm) baking dish or quiche pan with parchment paper and set aside.
In a medium skillet, combine a few tablespoons of water and then the mushrooms, bell pepper, zucchini, and red onion. Cook over medium-high heat, stirring frequently, until the vegetables are tender and the liquid has evaporated, about 10 minutes. Remove from the heat, add the tomatoes, and set aside.
In a blender, combine the chickpea flour, water, soy milk, nutritional yeast, lemon juice, miso paste, baking powder, onion powder, basil, fennel seeds, turmeric, and pippali. Blend until the batter is smooth.
In a large bowl, combine the vegetable mixture with the batter, then spread the mixture evenly in the prepared pie pan. Bake for about 30 minutes, or until firm and lightly browned on top and a knife inserted in the center of the frittata comes out clean. (You do not want any uncooked batter.) Remove from the oven and let it cool on a wire rack for 10 minutes before slicing. The frittata can be eaten warm or at room temperature.
Cover leftovers and refrigerate until needed. The frittata is best eaten within 3 days, but will keep for up to 5 days if properly stored. Reheat in a 350°F (175°C) oven for about 12 minutes or in the microwave for 2 minutes.