In a large Dutch oven or stockpot, heat the olive oil over medium heat and add the diced onion, celery, and carrots. Cook for 8 to 10 minutes until the veggies begin to soften.
Add the minced garlic and thyme and cook for one minute.
Add the diced tomatoes with the juice, tomato sauce, vegetable stock, diced yellow squash, bay leaf, and salt and pepper.
Turn the heat up to high and bring to a boil. Once boiling, lower the heat to a simmer and cook vegetables for 10-15 minutes or until the squash is tender.
Add the drained cannellini beans, frozen spinach, and pesto. Cook for 5 minutes more to warm the spinach and let the flavors blend.
Once the spinach is warmed through, add the cooked ditalini pasta and 2 tablespoons of balsamic vinegar.
Taste and add more salt and pepper if necessary.
Serve with a sprinkle of grated parmesan cheese.