Preheat your oven to 350°F (175°C) and lightly grease a 1 ½-quart casserole dish.
In a large pot of lightly salted water, cook the egg noodles for about 5 minutes, just until they’re almost tender. Drain them well and set aside.
Heat olive oil in a large skillet over medium heat. Add the chopped onion and sauté for 4–5 minutes until it becomes soft and translucent.
Stir in the cooked chicken, red bell pepper, celery, and chicken stock. Increase the heat slightly and bring the mixture to a gentle boil. Let it simmer for an additional 5 minutes.
Lower the heat and stir in the sour cream and oregano, mixing until everything is well combined.
Layer half of the chicken mixture into your prepared casserole dish. Arrange the fresh asparagus evenly on top.
Spread the cooked noodles over the asparagus, followed by about 5 tablespoons of Parmesan cheese sprinkled evenly.
Add the remaining chicken mixture on top of the noodles, spreading it out evenly. Finish it all off with the remaining 3 tablespoons of Parmesan cheese.
Place the dish into the preheated oven and bake for about 30 minutes, or until the top turns golden brown and bubbly. Serve warm and enjoy!