Mix the flour, salt and baking powder in a bowl.
Pour in the water and mix to make a dough.
Let it sit for 5 minutes.
Put the dough on a floured surface and break off golf ball-sized pieces.
Roll each one out to a ½-inch thick 6-inch round.
Heat the oil in a 2-inch deep pan and fry each bread disc until puffed up and golden.
Flip to cook the other side, then drain on paper towels.
Brown the beef with some salt and black pepper in a skillet, breaking it up with a wooden spoon as it cooks.
Add the beans and cook for 10 minutes.
Spread the meat mixture over the fry bread and top with tomatoes, lettuce and sour cream, then serve hot.