Poach and shred the chicken (skip if using rotisserie): Place 2 boneless skinless chicken breasts — only if making your own shredded chicken, skip if using rotisserie in a pot, cover with water, and add 1 chicken bouillon cube — only for poaching liquid, skip if using rotisserie. Bring to a boil, then reduce to a simmer for about 15 minutes or until internal temp reaches 165°F. Shred once cool enough to handle.
Sweat the onion: Heat 1 tablespoons oil, for sweating onions in a large pot over medium heat. Add 1 onion, diced and sweat until softened.
Add carrots and celery: Add 1 cups carrots, diced and 1 cups celery, diced, cooking until they start to soften.
Stir in 1 tablespoons garlic, minced and 1 tablespoons butter, cooking until fragrant.
Add 1 tablespoons Italian seasoning and 1 teaspoons lemon pepper.
Add stock and bring to a boil: Pour in 8 cups chicken stock and add 1 chicken bouillon cube (for the soup base). Bring to a boil.
Add noodles and turn off heat: Stir in 2 cups egg noodles, then turn off the heat — residual heat finishes cooking the noodles without turning them mushy.
Stir in the chicken: Add 2 cups shredded chicken — rotisserie, or see homemade option below (rotisserie or your homemade batch) and stir to combine. Taste and adjust seasoning before serving.