Place the chopped onion and oil in a skillet and saute until cooked, about 5 minutes.
In the same pan add the shredded turkey, cumin, pepper and water to the onions. Stir to mix spices and cook for 3 to 5 minutes so that the water evaporates.
Remove from heat once done. Season with salt if needed, it will depend on the original flavor of your turkey.
Place the cooked turkey into the taco shells (you can make your own by frying corn tortillas in hot oil and forming into a taco while they're still soft).
Top each taco with lettuce, tomato, shredded cheese, sour cream or anything extra you'd like. I'm a sucker for pickled carrots and jalapenos on my tacos.