Combine the olive oil, lemon juice, garlic, thyme, oregano, salt, and pepper in a container. Add the fish filets, turn to coat, and marinate, covered in the refrigerator, for 2 to 4 hours.
Heat a large skillet over medium-high heat. Cook the tortillas one at a time for 15 seconds on each side until pliable, browned in spots, and warmed through. Stack the tortillas on a plate as they are cooked, and cover with a clean dish towel to keep them warm.
Return the pan to medium-high heat. Remove the fish from the marinade, allowing excess to drip back into the container, and add the fish without crowding (cooking it in batches if necessary). Discard the marinade. Sauté until cooked through, turning it as needed, about 5 minutes in all. The pieces may fall apart a little as you cook them; that’s perfectly fine. Place them on a serving plate and use a fork to pull the pieces into bite-sized pieces.
Serve the fish, tortillas, and the toppings you like. Let everyone assemble their own tacos.
Notes
You can make the fish up to 2 days ahead of time and warm it in a pan over medium-low heat until warmed through.