In a large bowl mix all the ingredients for the meatballs: the grated carrots and zucchini, ground beef and sausage (remove the skin), egg, parmesan cheese, breadcrumbs, parsley and sea salt. Mix everything to combine well.
Roll with your hands small meatballs with 1 Tbsp of the mix.
In a large skillet, heat the olive oil and add the onion. Cook for 1/2 minutes at medium heat up until golden.
Add the meatballs and sear them nicely all around for 2/3 minutes.
Mix the tomato sauce with the milk, season with sea salt and add them all around the meatballs.
Reduce the heat to a simmer and cook uncovered for 15 min up until the sauce thickens. Serve warm and enjoy!