Heat a lightly oiled skillet over medium-high heat. Saute the turkey and onion until browned, about 8 minutes. Drain and discard juice.
Stir chile powder, garlic powder, and onion powder into the turkey mixture until well combined. Mix in salsa, green chile peppers, cilantro, salt, and pepper. Cook and occasionally stir taco filling until flavors meld, 7 to 10 minutes.
Fill taco shells with taco filling. Top with avocado, shredded Monterey Jack cheese, lettuce, and tomatoes.