One-Pan Italian Turkey Meatballs with Marinara

Make the Meatballs
2 Combine Panko breadcrumbs and milk in a large mixing bowl.
4 Let sit for 5 minutes to allow the breadcrumbs to soak up the liquid.
6 Set a small sheet pan, baking dish, or cutting board next to the bowl (this is where you will line up the meatballs as you shape them).
8 To the breadcrumbs / milk, add turkey, 2 Tablespoons  onion, 1 ½ teaspoons Italian Herb Seasoning, and egg. Add salt (1 teaspoon if your Italian Seasoning doesn't include salt; 1/2 teaspoon if your Italian Seasoning does include salt).
10 Using your hands, gently combine all of the ingredients, mixing them just until combined (but being careful not to over-mix).
12 Use a 1 Tablespoon measuring spoon to scoop up one heaping spoonful of the meatball mixture at a time and then roll it into a ball. (Don’t worry if they aren’t all perfect balls, but try to make them uniform in size so they cook evenly.)
14 Line up the meatballs on the prepared pan as you make them. (At this point, you can cover and refrigerate the meatballs to cook them later if you’d like.
Cook Meatballs
18 Heat a large Dutch oven, saute pan, or skillet over low-medium heat. Add oil and let it heat for a minute until shimmering. When oil is hot and shimmering, transfer the meatballs to the pan (I find it easiest to use my hands to quickly transfer the meatballs one-by-one).
20 Let the meatballs sear on the bottom for 2 minutes and then give them pan a gentle shake or use a spatula to gently turn them so that the meatballs start to roll around a bit (this will help them to hold their round shape).
22 Continue cooking meatballs, turning with a spatula or tongs, until meatballs are nearly cooked through. (Take one out of the pan and slice it open to be sure. It should be tender and juicy inside but not look pink.) It should take a total of 8 to 10 minutes to cook the meatballs.
24 Transfer the meatballs to a plate and return the pan to heat.
Make Sauce
28 If the pan looks dry, add a splash of oil. 
30 Add 3/4 cup onion. Saute until onion is tender and starting to brown in spots.
32 Add 1 ½ teaspoon Italian Herb Seasoning and tomato paste and stir for 1 minute. 
34 Pour crushed tomatoes into the pan and stir everything to combine.
36 Simmer sauce for 2 minutes to let the flavors come together. 
38 Add meatballs to sauce and cook everything together for 1 minute.
40 Serve meatballs over spaghetti (or spaghetti squash) or with bread on the side. Top with parmesan and chopped parsley.