Begin by heating the tomato sauce over a low heat, covered, in a medium to large pot.
While sauce is heating, dice celery, carrots and onion; add to a large bowl. Generously sprinkle with salt and pepper and toss to combine. Mince the garlic and set aside.
In a medium skillet, heat cooking spray on medium heat. Once the pan is hot, add diced vegetables and minced garlic and sauté until vegetables start to soften and onions become translucent (about 5 - 7 minutes). Once soft, remove from heat and pour into the same large bowl, completely emptying skillet (reserve skillet). Let stand 5-10 minutes to cool slightly.
To the vegetables, add the breadcrumbs, cheese, garlic powder, onion powder, oregano, basil, parsely, salt and pepper. Mix all ingredients using a spoon, then add the meat. Combine with your hands, being careful not to over-knead while evenly incorporating all ingredients (if mixture seems slightly too wet, sprinkle in a little more breadcrumbs or cheese). Form meatballs into balls about 1 1/2 - 1 3/4" in diameter, and set aside on a piece of wax paper. Repeat with remaining meat mixture (should make around 14 - 18 or so meatballs).
To the same skillet*, add more cooking spray and heat on medium heat. Once hot, add meatballs, being careful not to overcrowd skillet (work in batches, if needed). Sear meatballs 3-5 minutes per side, gently flipping with tongs. Once both sides have seared, add par-cooked meatballs to your pot of sauce, cover. Repeat with remaining meatballs.
Simmer meatballs in sauce, covered, on low heat for 1-3 hours, and enjoy! (Serving Suggestion: my favorite way to serve these meatballs is over a bed of high fiber (such as Dreamfields) or whole wheat pasta with a scoop of low-fat ricotta cheese!).
* Though pan-searing the meatballs is the way to get the best results, if this is too labor-intensive or time consuming, you can par-bake the meatballs in the oven instead. After rolling the meat mixture into balls, place all of the balls 1/2"-1" apart on a baking sheet lined with foil and sprayed with cooking spray. Cook the meatballs for 15-30 minutes at 350º, flipping halfway through, then add them to the pot of sauce.