Heat olive oil in a dutch oven or large soup pot over medium heat. Add chopped onions and cook until soft and just beginning to brown (about 8 to 10 minutes), stirring frequently.
Add garlic, stirring constantly for an additional 30 seconds.
Add tomatoes and juices, chicken stock, sugar and bread crumbs. Season with salt and pepper. Bring to a gentle boil. Reduce heat as necessary to maintain a simmer (medium low). Cover and simmer for 20 minutes.
Remove from heat and very carefully purée tomato mixture using an immersion blender. If using a regular blender, purée in small batches and exercise caution.
Return tomato mixture to pot (if you used a blender to purée) . Pour in milk and stir well to combine. Bring back to a simmer. Add tortellini once simmering, cover and cook an additional 7 to 10 minutes (or as directed on package of tortellini).
Sprinkle with grated Parmesan cheese when serving (if desired).