For ground beef, cook it in a large skillet over medium-high heat, breaking it up, until it reaches 160°F (71°C), about 8 to 10 minutes. Drain excess fat.
Stir the taco seasoning and 1/2 cup water into the cooked beef and simmer 5 minutes. For the chicken option, combine cooked shredded chicken, taco seasoning, and 1/2 cup water in the skillet and heat for 5 to 7 minutes, until the chicken reaches 165°F (74°C) and the sauce thickens.
Warm taco shells according to package directions, or wrap tortillas in foil and heat in a 300°F oven for 10 minutes.
Arrange all toppings in separate bowls and set out on a table or counter with serving spoons.
Place the warm meat in a serving dish and set out with the shells and toppings.
Let guests build their own tacos with their preferred combination of ingredients, squeezing lime over the top.