I actually took this recipe straight form The Country Cook, but adjusted the amounts slightly for my tastes. When I say it's easy. I mean it!
1/2 cup mayonnaise
4 oz. cream cheese, room temp
1 tsp. italian seasoning
1 roll French bread or 2 sub rolls, sliced
1/2 Bag of frozen meatballs (I personally like ot bake my meatballs first to give them a crispy outside)
1 jar marinara
1 cup shredded mozzarella cheese
Preheat oven to 375 degrees. Spray a casserole dish with cooking spray, then lay your bread slices down flat, ripping a few into smaller pieces to fill in the gaps.
Mix together the cream cheese, mayo and seasoning. Spread over the bread slices. I preferred a little less of this mixture than the original, so I just focused on getting a little of it on each slice. Just like a meatball sub, I wanted less mayo than the marinara. The original recipe used almost equal amounts, and that through off the ratios of what you'd actually get in a meatball sub.
Add your meatballs and pour on the marinara. Add mozzarella cheese and bake for 30-40 minutes, or until cheese starts to brown.
This works really well as a freezer meal too. Plan on making spaghetti and meatballs, but buy 2 jars of marinara. Assemble the casserole and just place in the freezer until ready to cook. You will need to double the cooking time if you don't thaw before baking.