Add more oil to the pan if it seems dry, then add the onions, carrots, celery, garlic, salt, and pepper and cook, stirring, until the veggies are tender, about 6 minutes.
Add the acini di pepe and cook, tossing to lightly toast, 1 to 2 minutes. Pour in the white wine and scape up any browned bits on the bottom of the pan. Add the broth and pesto and stir until well incorporated into the soup.
Add the meatballs and any of their juices back into the pot along with the cheese rind and bring to a rapid simmer, 3 to 4 minutes. Once simmering rapidly, reduce the heat so that it is just gently simmering. Cover and cook, simmering gently, until the pasta is tender and the meatballs are fully cooked, 6 to 8 minutes.
Remove the cheese rind and stir in the lemon juice. Taste and adjust seasonings, if desired.
To serve, ladle the soup into bowls. Finish with fresh basil, more grated Parmesan, and a few cracks of black pepper. Enjoy!