In a small bowl, combine water, soy sauce, salt, brown sugar, onion powder, liquid smoke, black pepper, and chili powder.
Pour the mixture over the chicken breasts and marinate overnight.
Cook chicken on barbecue or indoor grill over medium/high heat for 5 to 6 minutes per side or until done.
Slice chicken into bite-size chunks.
Heat the tortillas in a steamer or wrap them in a moist towel and heat for about 30 seconds in the microwave.
Spread about ¼ cup of chicken down the middle of one of the flour tortillas.
Sprinkle about 2 tablespoons of lettuce over the chicken.
Sprinkle a heaping tablespoon of cheese over the lettuce.
Finish the taco by stacking a heaping tablespoon of diced tomato on the cheese, then fold up the edges of the taco, and serve immediately. Repeat with the remaining ingredients.
