Preheat an oven to 200C (400F), and line a baking pan with parchment paper. Place half of the onions and the ground meat, parsley, bread crumbs, salt, pepper and allspice in a medium-sized bowl. Mix the meat mixture thoroughly, and form into balls the size of walnuts. Place on the baking pan and bake for 10 minutes. Remove the meatballs from the pan and drain on a paper towel. Set aside.
Meanwhile, pick any stones from the lentils, place in bowl, cover with cold water, and drain.
Break the angel hair pasta into the soup and add the meatballs. Simmer slowly for another 5-10 minutes or until the lentils and noodles are cooked, adding more chicken broth or water as needed. Just before serving, squeeze some lemon juice into soup.