Make the mushroom marinara by heating the olive oil in a large Dutch oven over medium heat. Add the onions and mushrooms and saute until tender; add the garlic and cook for 60 seconds, stirring frequently.
Add the remaining ingredients; cover with a lid and simmer for at least 2 hours, stirring occasionally.
Taste and re-season, as needed.
Make the meatballs by putting the onions, garlic, and mushrooms in a food processor to chop, otherwise, chop them as small as you can. Combine all ingredients (except for olive oil) together gently.
Form into small meatballs and set aside.
Cook the meatballs by heating a large skillet over medium heat with 1 tsp olive oil. Cook the meatballs until golden brown on all sides.
Remove from the skillet and place the cooked meatballs in the mushroom marinara.
Preheat the oven to 350 degrees.
Cook the pasta in a large pot of well-salted water to al dente, per the instructions; drain.
Pour the pasta into the sauce with the meatballs. Add the fresh basil and cheese–reserving a bit for the top, then mix VERY gently.
Bake the dish by topping with remaining cheese then place into the oven to bake for 20-25 minutes.
Remove from the oven and top with remaining basil and parmesan. Enjoy!