In a pot, heat the oil over medium heat. Add the onion and garlic and cook, stirring occasionally, until soft but not browned, about 3 minutes.
Add the broth, tomatoes, sugar, thyme, and season with salt and pepper. Bring to a low boil for 15 minutes, stirring occasionally.
Using an immersion blender or stand up blender puree the soup (in batches if needed) until it is smooth. Stir in the spinach until it is wilted. Season with salt and pepper. Serve with crackers.