Optional step: add the diced onion to a pan with a little oil and saute until no longer raw; remove from heat onto small plate and cool in freezer while assembling other meatball ingredients.
Add beef, onions, almond flour, tomato paste, egg, cilantro and seasonings to bowl. Mix so ingredients are evenly distributed and form into approximately 12 – 13 meatballs, each weighing about 1.5 oz.
Place meatballs on a lined baking tray and put in oven on middle shelf for 15 minutes.
Meanwhile, get the sauce ready. Optional step: drain the tomato sauce of any excess liquid through a fine meshed sieve.
Add sauce to pan to heat through and reduce; add salsa to taste and simmer gently to thicken.
When meatballs are ready, remove from oven. Remove them from the baking tray and place in small deep baking dish (8″x8″ is good). Cover with thickened tomato sauce; return to oven for 10 minutes.
While meatballs are in the oven, julienne zucchini (avoiding the seeds). Add to a medium-hot large skillet with a little oil. Stir fry until they have softened enough to twirl around a fork but still retain crunch. Season to taste.
Remove meatballs from the oven and stir through the sauce.
Serve the meatballs and sauce on top of the zucchini noodles.