Drain the mushrooms and then place them in a pan over medium heat to saute them. After about 10 minutes, remove them from the heat and allow to cool. Chop the mushrooms to fairly small pieces.
Saute the minced onions and green peppers.
Combine the bread crumbs, cheese and spices.
In a large bowl combine the meat, eggs and all other ingredients.
Mix the dry mixture into the meat and stir to combine well.
Form them into meatballs. The size is up to you, smaller ones will cook a bit faster if your in a rush.
Sear the meatballs to give them a crust prior to placing them in the oven. This is optional but gives a nice bit of texture to the meatballs.
Place the mushroom meatballs into a baking dish and cover with diced tomatoes and marinara sauce.
Bake at 350 for about 45 minutes.