Slice sausages 1 cm thick. Using a large saucepan, brown sausages. (If turkey, spray pan first with vegetable spray.) Pour off any fat. Add celery, zucchini and onion. Saute` 2 minutes, stirring. Put stock, tomato sauce and basil into crockery pot and mix. Heat on HIGH (300) for 30 minutes. Add sausage-vegetable mixture to crockery pot. Turn to low and cook 2 to 3 hours. Salt and pepper to taste. Ladle into bowls and garnish with grated cheese.