Heat olive oil in a large skillet over medium-high heat. Add chicken and cook until golden brown and cooked through, about 8 minutes. Remove from heat and set aside.
In the same skillet, add the onions and cook until softened, about 5 minutes. Add the taco seasoning and stir to combine.
Shred the chicken with two forks or with your hands. Add to the skillet and mix everything together.