Make the meatballs by placing the ground chicken in a bowl (with the spinach if using it). Add the garlic, onion, bread crumbs, Parmesan, nutmeg, salt, pepper, parsley (if using), and 2 tablespoons of the tomato paste. In a separate bowl using a fork, gently combine the milk and egg. Add this to the rest of the meatball mixture and combine. You don't want to overmix but you do want it evenly mixed together.
Combine the remaining tomato paste and the olive oil to make a “glaze” to brush over the meatballs. It’s best to put the meatballs on a parchment lined baking sheet first and then glaze them or you may find they stick and are difficult to remove especially once glazed. Bake the meatballs in your oven for about 18-20 minutes at 325 degrees F until cooked through.
In the meantime, I heated up my spaghetti sauce on the stove and I began boiling water and cooking my pasta. Drain the pasta, saving 1 cup of the pasta water. Toss your spaghetti with the sauce, adding in some of the reserved pasta water if needed to get the right consistency. I know some people who like to throw a pat of butter in there while tossing the pasta - I have never felt it needed it and why add extra fat but you can try it for yourself. Serve the pasta with the meatballs and sprinkle some extra Parmesan over the top if desired.
The nutritional information listed here includes the spinach and parsley. Obviously, the calorie content will be slightly higher with those but the nutritional content will be boosted too.
You may also find that you'd like to make a little more spaghetti and serve this to 8 people instead of 6 - it's easy to stretch it that way! Other options include substituting zucchini "noodles" or spaghetti squash for the typical pasta.