Mix breadcrumbs and milk in a large bowl and let them stand while you prepare the rest of the ingredients.
Heat oil over medium in a saucepan. Cook onion with ¼ tsp salt until soft, about 7 minutes.
Add garlic and cook until fragrant, about a minute. Let cool slightly, then add to the breadcrumb mixture.
Stir in mayo, parsley, the rest of the salt, pepper, and cayenne.
Once cool, mix in the eggs, then the turkey. Be gentle but thorough.
Shape the mix into a loaf on a parchment-lined baking sheet.
Bake for about 1 hour or until the inside temperature reaches 165ºF. Let it rest before slicing.
Notes
Letting the breadcrumb mixture sit with the milk helps ensure a moist meatloaf.
Cooking the onions and garlic before adding them to the mix brings out their flavors.
Letting the meatloaf rest before slicing makes it easier to cut and serves up more juicy.
To add a meatloaf glaze: About 25 minutes into baking your meatloaf, remove it from the oven and spread the glaze evenly and thickly over the top then finish baking.