Boil spaghetti according to package directions. Also, heat the meatballs in a microwave or in the oven until heated through.
Meanwhile, in a food processor, chop the Parmesan cheese, spinach and almonds on high power for about 1 minute, or until the whole mixture has been combined well.
Add the salt, olive oil and lemon juice and process again on high speed until the mixture is smooth, about 2 minutes. Scrape the bowl and process again as needed.
Once the pasta is done, drain it and immediately toss with the lemon spinach pesto. Add the meatballs and toss again.
Notes
You can substitute arugula, kale, or basil for the spinach.
Cashews or pine nuts can also be substituted for the almonds.