Heat olive oil over medium-low heat in a medium sized pan. Add garlic and onion saute until onions are translucent, 3 minutes. Add tomato paste, stir to combine. Add tomatoes, salt and oregano stir and simmer on low heat for 30 minutes.
Preheat oven to 400F. Line a sheet tray with foil and lightly coat with oil and set aside.
In a large bowl combine chicken, egg, garlic, chopped spinach, panko bread crumbs, milk, parmesan cheese, salt, and pepper.
Roll meatballs in 12 equal portions, about 1 1/2 inches, 2 to 3 tablespoons in size. Evenly space the meatballs on the baking sheet.
Place pan in the center of the oven and bake for 20 minutes.
Turn oven to broil and cook meatballs another 2 to 3 minutes, until the meatballs are golden brown on top. Serve meatballs with sauce.