Place black beans and black-eyed peas in a colander. Rinse under cold running water until clean. Drain completely and set aside to remove excess moisture.
If using frozen corn, allow it to thaw fully and pat dry with a paper towel. If using canned corn, drain thoroughly before use.
Dice cherry tomatoes into small, even pieces. Cut bell pepper into small cubes. Finely chop red onion to ensure it blends well with the mixture.
Cut avocado into medium-sized chunks. Chop cilantro finely and set both aside for later use.
In a large mixing bowl, add the drained beans, black-eyed peas, corn, diced tomatoes, bell pepper, and chopped onion. Stir gently to combine all ingredients evenly.
In a separate small bowl, add olive oil, lime juice, apple cider vinegar, sugar, salt, and black pepper. Whisk thoroughly until the dressing is fully combined and slightly emulsified.
Pour the prepared dressing over the bean and vegetable mixture. Toss gently but thoroughly to ensure all ingredients are evenly coated with the dressing.
Add diced avocado and chopped cilantro to the bowl. Fold them in gently to avoid mashing the avocado while still distributing evenly.
Cover the bowl with a lid or plastic wrap and refrigerate for at least 30 minutes. This allows the flavors to blend and develop.
Before serving, stir gently and taste. Adjust seasoning if needed by adding more lime juice, salt, or pepper. Serve chilled.