Preheat oven to 180 degrees C. Lightly grease a casserole dish.
Cook noodles in a large pot of boiling water for 5 minutes or until almost tender. Drain and rinse under cold water.
Heat the olive oil in a heavy frypan over medium heat. Cook onion for 4 to 5 minutes, stirring frequently. Add chicken, red capsicum, celery and chicken stock. Bring to a boil and simmer for 5 minutes. Stir in sour cream and oregano.
Spread half of the chicken mixture into the prepared dish. Arrange asparagus over chicken, spread cooked noodles evenly over asparagus and top with the remaining chicken mixture. Sprinkle with Parmesan cheese.
Bake 30 minutes in the preheated oven, until lightly brown.