*Can use more than one green chile (to taste) and leave out additional heat from red chile powder
Preheat oven to 350 degrees. Heat butter or oil in oven-proof or cast iron pan (if planning on also baking in the oven). (Option to use reguar heavy-bottom pan if only cooking on stovetop.) Add onions and sautee for about 5 minutes until they are soft and translucent. Add chopped ginger and green chile and cook for another couple of minutes. To this, add mushrooms and cook until all water with mushrooms reduces. Mix in bell pepper, turmeric, garam masala, curry powder, salt, black pepper, and cilantro leaves. Continue cooking this mixture.
Meanwhile, in a separate bowl, add eggs and milk, and season with salt and pepper. Keep in mind that the onion mixture also has salt and pepper. Beat well.
Reduce heat to medium-low and add egg mixture to the pan with the onion and mushrooms. Shake the pan to distrubute evenly. Let this cook on low heat for 5-6 minutes undisturbed. You can either continue to cook the frittata on the stovetop until the center is set (about 10-12 minutes) or place the pan on the middle rack of the oven for 20-25 mintues.
Serve Masala Frittata with tomato ketchup or hot sauce drizzled on top.