Preheat oven to 400°F / 200°C.
Line taco shells open-side up on a sheet pan or in a baking dish, propping them up against one another so they sit upright. (Note: Be sure to use a sheet pan with sides so that the shells don't slide off or use a baking dish. Depending on the brand / shape of taco shell, you may need to play around with how you arrange them - some will easily sit upright as in the photos, but some will work better if you arrange may need to be leaning against one another at an angle. If the tacos aren’t supported by the end of the pan, use a piece of aluminum foil rolled into a ball and then pressed flat to support the end of the row. It doesn’t need to look perfect - just be sure that you can spoon filling into each taco.)
Make taco meat: Heat oil in a large skillet over medium-high heat. Add ground beef, chili powder, cumin, paprika, garlic powder, salt, and black pepper. Saute, breaking the meat apart, until cooked through, 6 to 8 minutes. Add water and stir well to combine. Continue cooking until water is cooked off and meat is tender, 2 to 3 minutes more.
Assemble tacos: Spoon ground beef into tacos. Top with cheese.
Bake: Bake tacos until cheese is melted and taco shells are golden brown and crisp, 5 to 7 minutes.
Remove tacos and fill with lettuce, sour cream, chopped tomato, and salsa.