Meatballs - Preheat oven to 375F and line a baking sheet with foil for easier cleanup and spray with cooking spray, or spray the baking sheet.

To a large bowl, add all the ingredients, and using clean hands or a wooden spoon, gently mix together all the ingredients. Tip - Do not overmix or overwork the meat mixture because the finished meatballs will be tougher.

Using a 1 to 2 tablespoon scoop (often labeled as 'medium' size), form approximately 32 meatballs.

Evenly space them on the prepared baking sheet and bake for about 15 minutes, or until done. Baking Tips - Being that the meatballs are fairly small, they likely won't take more than 15 minutes to bake through, but all ovens vary, and if your meatballs are slightly larger, they may take up to 20 minutes to bake. Bake until done, whatever that means in your oven and situation.

Casserole - Spray a 2.5 to 3-quart casserole or baking dish (or 9x13-inch pan) with cooking spray and place the cooked meatballs into the dish. Make-Ahead Tip - If you're making this in advance, this is the most logical place to stop, cover well, and refrigerate for up to 48 hours before continuing on with the rest of the recipe and baking it off fully.

Evenly drizzle the marinara sauce over the top.

Evenly sprinkle both the mozzarella and Parmesan cheese over the top.

Bake uncovered for about 10 to 15 minutes, or until the cheese has melted and is as lightly golden browned as desired.

Optionally garnish with fresh herbs and serve immediately.

Storage - Leftover casserole will keep airtight in the fridge for up to 5 days or in the freezer for up to 3 months. Reheat leftovers for about 30 seconds in the microwave, or as desired.