Place the red onion in a bowl of cold water and soak for 10 minutes. Drain and set aside.
In a large bowl, whisk together the mayonnaise, sour cream, cilantro, cumin, chili powder, and lime juice. Season with salt and pepper to taste.
Add the red onion, bell pepper, jalapeno, and chicken to the bowl and give it a good stir to combine. Taste, and adjust seasonings if needed, adding a little extra lime or spices to your taste.
Serve the chicken salad on bread, salad greens, or on top of a halved avocado.