In a large Dutch oven or soup pot, heat the olive oil over medium heat. Add the onions, celery, carrots, 1 teaspoon salt, and 1/2 teaspoon pepper. Cook, stirring occasionally, until the vegetables are softened and the onion is translucent, 6 to 8 minutes.
Add the garlic and Calabrian chili peppers and cook until fragrant, about 1 minute. Add the tomato paste and cook, stirring constantly, until it darkens to a deep red and coats the vegetables, 1 to 2 minutes more.
Pour in the white wine and scrape any browned bits from the bottom of the pot. Simmer until the wine has reduced by about half, about 2 minutes.
Stir in the chicken broth, diced tomatoes (with their juices), lemon zest, Italian seasoning, garlic powder, bay leaf, and Parmesan rind. Increase the heat to high and bring to a boil, 10 to 12 minutes.
When the soup comes to a boil, reduce the heat to a steady simmer (about medium heat). Add the chicken thighs along with the remaining 1½ teaspoons salt and 1/2 teaspoon pepper. Cook, uncovered and simmering steadily, for about 8 minutes.
Stir in the potatoes and the ditalini and continue to cook, simmering uncovered, for about 10 minutes, or until the chicken is cooked through, the potatoes are fork tender, and the pasta is al dente.
Transfer the chicken to a cutting board and shred it with two forks. Return the shredded chicken to the pot and discard the bay leaf and Parmesan rind.
Remove the pot from the heat. Stir in the lemon juice and parsley. Taste and adjust with more salt and pepper.
Ladle into bowls and finish each with a generous shower of grated Parmesan cheese.