Squeeze the sausage meat from its casings into bite-sized chunks. Heat 1 tablespoon of olive oil in a large saucepan or Dutch oven over a medium heat. Add the sausage meat pieces. Cook the sausage until browned all over. Remove from the pan with a slotted spoon and set to one side.
While the sausage meat is cooking, add ½ tablespoon of olive oil to a skillet over a medium/high heat. Add the bacon, cook through until golden and crisp. Remove from the pan with a slotted spoon and set to one side. Once cool enough to handle, crumble into bite-sized chunks.
Finely dice the onion and thinly slice the garlic. Dice the tomato, celery and zucchini. Add the prepared vegetables to the saucepan that cooked the sausage meat. Sweat gently for 2-3 minutes until just tender, adding additional oil if the pan is a little dry.
Add the chili flakes and stock to the saucepan. Bring up to a gentle boil then reduce to a simmer. You may use an alternative stock if desired, such as vegetable. You may also adjust the level of spice to suit your personal preference. You can season with salt and pepper if needed, this will depend on the level of seasoning already in your stock.
Return the sausage pieces to the saucepan. Continue to simmer for a further five minutes. The sausage meat should be hot through and the vegetables tender.
Tear the kale leaves into the soup. Cook through briefly until the leaves are just wilted. Remove the soup from the heat and stir through the heavy cream.
Divide the soup between four individual serving bowls. Top each bowl with the crispy bacon pieces. Serve hot with Keto toasted bread if desired.