Preheat the oven to 350F.
In the meantime, heat oil in a frying pan and saute onion until softened. Add the potato, chilies, a bit of salt, pepper and saute until cooked.
Grease a casserole dish with non-stick cooking spray and layer the dish with bread cubes, followed by the sautéed mixture, followed by tomato slices (add as many layers as you’d like).
Top it off with a layer of cheese.
In a bowl, whisk eggs, milk, sour cream, cilantro and seasoning until the mixture is fluffy.
Pour the mixture over the casserole dish.
Bake for 40-45 minutes or until the top is golden brown. Test by inserting a knife in the middle, if it comes out clean then the casserole is done.
Remove the casserole, let it cool for about 5-10 minutes.
Garnish with cilantro and scallion onions, slice and serve!