Preheat oven to 350 degrees Fahrenheit (175 degrees Celsius).

Remove corned beef from the pickling bag and place it in a baking pan. Cover with water, cover the pan, and bake for one hour. Remove pan from the oven, allow to cool slightly, then cut into cubes and set aside.

In a 10-quart pot, heat the olive oil over medium heat. Add diced onions, carrots, and celery, and sauté for five minutes, stirring occasionally until slightly softened. Stir in the flour, mustard, Worcestershire sauce, and apricot jam, mixing well to coat the vegetables. Season with salt and pepper to taste.

Add enough chicken or beef stock or chicken soup mix dissolved in water to fill the pot halfway. Add the cabbage, potatoes, and cubed corned beef. Pour in additional liquid so the pot is about three-quarters full. Bring to a simmer and cook for two and 1/2 to three hours, until the vegetables are tender and the flavors are well-developed.

Increase the heat and bring the soup to a boil. Add orzo and cook over medium heat for 30 minutes, stirring occasionally. Stir in the frozen peas and cook for an additional five minutes. Taste and adjust seasoning if needed.

Turn off the heat and allow soup to rest for a few minutes before serving.