Step 1: Prepare all vegetables: finely dice the red bell pepper, green bell pepper, red onion, Roma tomatoes, and jalapeño (if using). For a milder red onion flavor, soak diced onion in cold water for 10 minutes, then drain and pat dry.
Step 2: Rinse and drain the black beans and corn thoroughly. Place them in a fine-mesh colander and rinse under cold water until the water runs clear, then pat dry gently.
Step 3: In a large mixing bowl, combine the rinsed black beans, corn, diced red and green bell peppers, red onion, tomatoes, and chopped cilantro. Gently toss to combine.
Step 4: In a separate small bowl, whisk together the olive oil, fresh lime juice, minced garlic, ground cumin, chili powder, salt, and black pepper. Taste and adjust seasoning as desired.
Step 5: Pour the dressing over the vegetable mixture. Toss gently until all ingredients are well coated. Cover the bowl and refrigerate for at least 30 minutes to allow the flavors to meld.
Step 6: Just before serving, dice the ripe avocados and gently fold them into the chilled cowboy caviar. Give it a final taste and adjust seasonings if needed. Serve immediately with tortilla chips, as a side, or as a topping.