Oh, lots of options! You can simmer cauliflower and white beans in marinara - really yummy but you have to let the caulflower cook until it's almost falling apart. My DS in more innocent days said "Mommy, what are these white meatballs!"
There's a recipe for ricotta meatballs that looks good:
https://cooking.nytimes.com/recipes/1023488-ricotta-polpette-in-tomato-sauce
And chickpeas simmered in marinara is a classic - aka chana masala - but just use Italian spices instead. Make sure to cook for long enough until the chickpeas are super tender.