Heat 2 tablespoons olive oil in a small pot over medium-high heat. Place the onion, celery, shiitake mushrooms and curry paste in the pot. Add the sausage and continue to cook for 2 minutes. Cook for 4 minutes and then add the chicken stock, salt and pepper. Simmer soup for 10 minutes and then add the coconut milk. Cook for 3 minutes. Garnish soup with the cilantro.