Place the water, onion, leeks, tomatoes and their juice, carrots, acorn squash, and potatoes in the slow cooker. Tie the fresh herbs and parsley together with kitchen twine to make a bouquet garni. Add the bouquet garni and beans to the cooker. Cover and cook on low for about 6 hours.
While it's cooking, make the pesto. Add the garlic to a food processor and chop until fine. Add the basil and Parmesan cheese. While the motor is running, slowly add the olive oil and then the creme fraiche. Process until smooth and then store in the fridge until ready.
When the vegetables are tender, add the celery, celery leaves, green beans, zucchini, and cabbage to the slow cooker. Cover and cook for an additional hour.
Make the croutons by heating the oil in a large skillet over medium-high heat. Swirl the oil around to make sure it covers the bottom of the pan. Chop the bread into bite size pieces and add to skillet. Toast tossing the cubes, until well browned. Remove and let rest on a paper towel.
Remove the bouquet garni from the soup and season with salt and pepper. Serve with pesto and croutons on top.