Preheat oven to 400 degrees. Line a baking sheet with parchment paper.
Mix all the meatball ingredients (except the avocado) together in a large bowl. Divide meat mixture into 14 portions and cut avocado into 14 pieces. Place 1 piece avocado in center of each meat portion and gently shape into ball. Bake for about 30 minutes, or until browned and no longer pink inside.
Meanwhile, combine all ingredients for the sauce in a saucepan. Bring to a boil over medium-high heat, stirring frequently to prevent sticking. Reduce heat and simmer for 10 minutes, or until sauce thickens, stirring occasionally.
Add meatballs to the sauce and gently stir to evenly coat. Cook for 1-2 min, stirring frequently. Remove from heat. Serve over spaghetti, rice, or mashed potatoes. Garnish with additional chopped scallion, if desired. Enjoy!