Preheat the oven to 350°F. Lightly grease a 9x13-inch casserole dish with nonstick spray and set aside.
In a 5-quart pot, bring water to a boil and add the egg noodles. Cook until al dente, stirring every few minutes.
While the pasta water comes to a boil, place a large skillet over medium heat. Add the olive oil, diced ham, onion, and red bell pepper. Season with a little ground black pepper, and sauté until the onions are slightly golden brown and translucent.
In a food processor, use the cheese shredding attachment to shred the Swiss cheese; set aside. (Alternatively, grate by hand using a box grater).
In a small bowl, combine the sour cream, mustard, and an additional pinch of black pepper.
Drain the egg noodles well and add them to the prepared casserole dish.
Pour the sautéed ham and veggies over the noodles, reserving a ½ cup of the ham and veggie mixture for the topping. Add half of the shredded Swiss cheese and the sour cream sauce. Toss everything together until evenly combined.
Top the casserole with the remaining Swiss cheese, and sprinkle the reserved ham, peppers, and onions evenly over the top.
Bake uncovered for 15 minutes.
Carefully remove the casserole from the oven and sprinkle the fried onion strings over the top. Return the dish to the oven and bake for an additional 5 minutes until the cheese is melted and bubbly. Serve warm!