Preheat oven to 425°F (220°C). Line a large sheet pan with parchment paper or foil.
In a large bowl, combine ground meat, breadcrumbs, egg, garlic, Italian seasoning, salt, pepper, and Parmesan (if using).
Gently mix until just combined. Do not overmix.
Roll mixture into evenly sized meatballs and arrange on the sheet pan.
Drizzle meatballs lightly with olive oil.
Bake for 18–22 minutes, flipping once halfway, until browned and cooked through.
While meatballs bake, toss cherry tomatoes and red onion with olive oil, salt, and pepper. Set aside.
Make the green sauce by blending herbs, garlic, lemon juice, olive oil, salt, and pepper until smooth.
Remove meatballs from oven and let rest for 5 minutes.
Serve meatballs topped with tomato salad and drizzled with green sauce.