For the meatloaf: Preheat the oven to 350 degrees F.
Heat the olive oil in a small skillet over medium-high heat; add the garlic and onions and cook, stirring occasionally, until soft and brown, about 8 minutes. Transfer to a food processor along with the spinach, milk, lemon zest, mint, salt, Worcestershire, nutmeg, eggs, potato and some pepper. Pulse until everything is finely chopped and evenly mixed together.
Use a rubber spatula to transfer the spinach mixture to a bowl. Add the turkey and stir everything together. Transfer the meatloaf mixture to a 9-by-5-inch loaf pan (1 1/2 quarts) and bake until the mixture is cooked through, 1 hour 15 minutes. Let rest for 5 minutes.
For the tomato salad: Meanwhile, chop the tomatoes and toss with the olive oil, parsley and salt in a medium bowl.
Slice the meatloaf and serve it with the tomato salad.