In a large soup pot, combine the onion, carrot, and celery. Saute over medium heat until the vegetables start to turn golden brown around the edges, about 8-10 minutes. Add the garlic, dried basil, and dried thyme. Saute 1-2 more minutes, until the garlic is aromatic.
Add the tomatoes, vegetable stock, and beans. Cover and bring to a boil. Reduce the heat to a simmer.
Simmer for 25 minutes, until the flavors come together.
Remove the lid, and stir in the spinach. Cook 1-2 more minutes, just until the spinach is wilted. Turn off the heat. Season with salt and pepper.