Place chicken thighs in a food processor, and pulse until meat is coarsely ground.
Add bread, milk, egg white, cheese, oregano, 1 teaspoon salt, and 1/4 teaspoon pepper; process until meat is finely ground.
With moistened hands, shape mixture into 12 meatballs. In a large nonstick skillet, heat oil over medium heat. Add meatballs, and cook until golden brown, about 5 minutes.
Add tomatoes and puree, breaking them up with your fingers; bring to a boil. Reduce heat to a simmer; cover, and cook 15 minutes. Uncover; simmer until meatballs are cooked through, about 15 minutes more.
Serve these meatballs over Spaghetti Squash with Garlic for a virtuous take on spaghetti and meatballs.