Sift together the flour, salt, powdered milk, and baking powder into a large bowl. Pour the water over the flour mixture all at once and stir the dough with a fork until it starts to form one big clump.
Flour your hands. Using your hands, begin to mix the dough, trying to get all the flour into the mixture to form a ball.
NOTE: You want to mix this well, but you do NOT want to knead it. Kneading it will make for a heavy Fry Bread when cooked. The inside of the dough ball should still be sticky after it is formed, while the outside will be well floured.
Cut the dough into four (4) pieces. Using your floured hands, shape, stretch, pat, and form a disk of about 5 to 7 inches in diameter.
Use a large dutch oven and heat about 1 inch of vegetable oil to 350°F (If you don't have a thermometer you can tell if the oil is ready for each batch when a un-popped popcorn kernel is dropped in and pops immediately!).
Take the formed dough and gently place it into the oil, being careful not to splatter the hot oil. Press down on the dough as it fries so the top is submersed into the hot oil. Fry until brown, and then flip to fry the other side. Each side will take about 3 to 4 minutes.
The bread can be kept warm in a 200°F oven for up to 1 hour. They refrigerate well and can be reheated in a 350°F oven for 10 to 15 minutes before serving.
Make the Tacos:
In a large frying pan over medium-high heat, brown ground meat and onions until cooked; add salt and pepper to taste. Remove from heat.
Place Fry Bread, cupped side up, on separate plates. Layer ground meat, lettuce, tomatoes, Cheddar cheese, and green chiles onto top of each Fry Brad. Top with sour cream, if desired.