Sauté (Optional): In a large pot or Dutch oven, heat a little olive oil over medium heat. Add the chopped onion and cook until softened (about 5 minutes).
Add Ingredients: Place the raw chicken breasts in the pot. Add the taco seasoning, Rotel, black beans, corn, and chicken broth.
Simmer: Bring the mixture to a boil, then reduce heat to a low simmer. Cover and cook for about 20-25 minutes, or until the chicken is cooked through (internal temperature $165^\circ\text{F}$ / $74^\circ\text{C}$).
Shred & Finish: Remove the chicken, shred it, and return it to the soup. Stir in cream cheese or cream if desired.
Serve: Garnish and serve immediately as directed above.