In a large skillet, heat the olive oil over medium heat. Add the diced onion and sauté for about 3-4 minutes until softened. Add the minced garlic and cook for an additional minute until fragrant.

Add the ground beef to the skillet. Cook, breaking it apart with a spoon, until browned and cooked through, about 5-7 minutes. Drain any excess fat if necessary.

Stir in the diced tomatoes (with juice), beef broth, orzo, Italian seasoning, salt, and black pepper. Bring the mixture to a boil, then reduce the heat to low. Cover and simmer for about 10-12 minutes, or until the orzo is tender and has absorbed most of the liquid, stirring occasionally.

Once the orzo is cooked, remove the skillet from heat. Sprinkle the shredded mozzarella cheese on top, cover, and let it sit for 5 minutes until the cheese is melted.

Garnish with fresh basil if desired and serve warm.