Heat olive oil in a skillet over medium heat.
Add diced onion and cook until soft, about 3 minutes.
Add ground turkey, season with salt and pepper, and cook until browned.
Sprinkle in taco seasoning and pour in water. Stir and let simmer for 5 minutes.
While the turkey cooks, scoop a small amount from the center of each avocado to make room for filling.
Spoon the turkey mixture into the avocados.
Top with diced tomatoes, shredded cheese, and a dollop of sour cream.
Garnish with chopped cilantro and serve immediately.