Preheat the oven to 350 degrees F.
Combine the flour, sugar, and salt in a large bowl and stir briefly until the mixture is aerated. Using a pastry blender or your fingers, add the butter into the dry ingredients and cut the butter into the flour until the mixture has only pea-size pieces that are slightly yellow in color. This will take 4 to 5 minutes. Drizzle in 4 tablespoons of the ice water and mix just until the dough comes together (add the last tablespoon of ice water if necessary, but don’t overwork the dough or it’ll become tough). Shape the dough into a flat disk, cover it in plastic wrap, and refrigerate for at least 30 minutes.
After refrigerating, spray a deep dish pie plate or quiche pan with nonstick cooking spray and spread out the dough in the plate/pan evenly.
In a large skillet over medium heat, melt the butter. Then, sauté the green onions and peppers until tender, about 3 minutes. Stir in the cilantro.
In a medium bowl, whisk together the eggs and milk; add the flour, baking powder, and salt, and continue whisking until smooth. Stir in the cooked vegetables, the turkey, and about 2/3 cup of the cheese. Pour into the prepared pie plate. Top with tomato slices, sprinkle lightly with salt and pepper, then top with the remaining shredded cheese. Bake until the top is golden brown, 45 minutes to 1 hour.