Preheat oven to 350°F. Bring a large pot of salted water to a boil. Cook lasagna noodles for 8 minutes, strain, rinse with cool water, and set aside. Cook the whole box so you have extra.
Meanwhile, combine ricotta filling ingredients in a bowl and mix well. Set aside.
Heat oil over medium heat in a 12-inch cast iron skillet. Cook onions until softened, about 4 minutes. Add beef and pork and cook until browned and no longer pink. Use the tip of a spatula to break up the meat into very small chunks.
Discard some of the fat if desired and add the marinara, garlic, and tomato paste. Simmer for 5-7 minutes until sauce is slightly thickened.
Transfer the meat sauce to a large bowl, reserving about one cup in the skillet. Evenly spread to coat the bottom of the pan. Add a little more if needed.
Top with a layer of noodles without overlapping. Trim the noodles with kitchen shears to fit the circular shape (it does not need to be perfect). Layer with 1/3 of the ricotta. Repeat twice more starting with meat sauce.
Finish lasagna with a final layer of noodles over the ricotta and another layer of sauce. Cover with aluminum foil and bake for 45 minutes.
Remove from oven, top with fresh mozzarella, and return to the oven uncovered for another 15 minutes. Broil for the last 1-2 minutes to give the cheese a golden finish.
Let rest for 15 minutes before cutting so the lasagna can set. Garnish with fresh chopped parsley and serve.