Heat olive oil in a large skillet over medium-high heat. Sear chicken breasts for 3-4 minutes on each side until browned.
Sprinkle taco seasoning over the chicken and add 1/2 cup of water. Bring to a simmer, then cover and cook on low for 20-25 minutes until the chicken shreds easily.
Remove chicken from skillet and shred it using two forks. Return it to the skillet, combine with any remaining sauce, and simmer for an additional 5-10 minutes.
Warm tortillas in a skillet or microwave before assembling.
Fill each tortilla with the shredded chicken and desired toppings.