HEAT the oil in a stock pot and sauté the onion, garlic and celery until tender. Add the tomatoes, lentils, VEGEMITE, thyme, and water and cover and simmer for 30 minutes.
UNCOVER, bring to the boil and add the pasta. Cook for 10 minutes or until the pasta is al dente.
SPREAD the toast with VEGEMITE then top with the cheese. Grill for 2-4 minutes until the cheese has melted. Spoon the soup into serving bowls and serve with toasts. Serve immediately.