Place the 2 packed cups diced bread in a large mixing bowl and cover with the 2 beaten eggs. (Push bread down so it all gets moistened.) Let soak until most of the egg is absorbed and bread is broken down, about 20 minutes.
Meanwhile, place the 2 cloves garlic and 1 teaspoon fennel seeds on a cutting board and sprinkle the 1/2 teaspoon pepper and 2 teaspoons salt on top. Chop mixture until it is a rough paste (it will resemble cornmeal).
Add the 1 pound ground beef and 1 pound ground pork to the bowl with the egg-bread mixture along with the 1/2 minced onion (save the other half for the sauce), 6 tablespoons chopped parsley, 1 tablespoon dried oregano, and garlic-fennel paste. Mix with your hands until evenly combined, breaking up any bread chunks.
Roll one small tester meatball. Heat the 2 tablespoons of oil in a large Dutch oven or soup pot over medium heat. Cook tester meatball until it is browned on all sides and cooked through. Taste the meatball. Is it perfect? Does it need more salt? Seasoning? Occasionally I will add more salt or even 1/2 teaspoon red chile flakes to the meatball mixture at this point.
Gather mixture into round balls, about 2 inches in diameter, using a cookie scoop if you have one, and place on a baking sheet. Make smaller or larger meatballs if you prefer.
Return the pot that you cooked the tester meatball in to medium heat and add meatballs in batches being careful not to crowd. Cook meatballs turning frequently until browned on all sides. You don't need to cook them all the way through at this point they will finish cooking in the sauce, just make sure they are nice and browned. Remove the meatballs to a clean bowl as they finish cooking and continue with the next batch until all meatballs are browned. Set aside while you make the sauce.