Rinse and drain the kidney beans thoroughly under cold running water. Pat dry with paper towels if possible.
In a large mixing bowl, combine the kidney beans, diced red onion, red bell pepper, corn kernels, and chopped cilantro.
In a small separate bowl, whisk together the lime juice, olive oil, salt, and pepper until well emulsified. Add optional garlic and cumin if using.
Pour the dressing over the bean mixture.
Toss everything gently but thoroughly, being careful not to mash the beans.
Taste and adjust the seasoning, adding more salt, pepper, or lime juice as needed.
If using optional ingredients like avocado or feta cheese, fold them in gently at the very end.
For best flavor, let the salad rest for at least 15-30 minutes before serving, or chill for a refreshing cold option.