Wring the spinach out well until it’s very dry. You should end up with about 1 cup [110 g].
Add the spinach to a mixing bowl along with the turkey, bread crumbs, Parmesan, milk, basil, garlic, and pepper (do not add the salt). Mix together until well combined.
Shape into 30 to 35 heaped meatballs, about 1 Tbsp each. Set on a plate as you shape them, then sprinkle evenly on the first side with half the salt.
Heat a large nonstick sauté pan or well-seasoned cast-iron skillet over medium heat. Once hot, add the oil, swirl to coat, and add the meatballs salty-side down. Sprinkle the other side with the rest of the salt. Cook until deeply golden brown on one side before turning. Rotate the meatballs every couple minutes, for a total of about 10 minutes. Once evenly seared, add the water to the pan, cover, and steam the meatballs for about 3 more minutes, until completely cooked through. Remove the lid and let the liquid reduce down while frequently shaking the pan to roll the meatballs around. Stop once the sauce glazes the meatballs, 2 to 3 minutes after removing the lid.