In a medium nonstick saucepan, heat a drizzle of olive oil over medium heat. Once the oil begins to shimmer, add the mushrooms and tomatoes and cook for 3-4 minutes, until they start to release their juices. Season with salt and pepper.
Add a bit more olive oil to the pan, then add the garlic and cook for 2 minutes, until fragrant.
Add the spinach and cook for 3-4 minutes, until wilted. Remove the pan from the heat.
In a medium bowl, combine the chickpea flour, nutritional yeast, baking soda, garlic powder, turmeric, salt, black salt, apple cider vinegar, and almond milk, and whisk together until mostly smooth.
In a medium nonstick saucepan, heat a drizzle of olive oil over medium heat. Once the oil begins to shimmer, add a ½ cup (120 ml) of the omelet batter to the pan. Let cook for 5-7 minutes, or until several bubbles have formed on the surface. Spoon half of the vegetable filling onto one side of the omelet.
Using a spatula, fold the omelet in half. Turn off the heat and cover the pan with a lid. Let the omelet steam for 5 minutes, until completely cooked through. Repeat with the remaining omelet batter and filling.