In a small mixing bowl, combine finely chopped red onion, freshly squeezed lime juice, and olive oil. Add a sprinkle of kosher salt and black pepper to taste. Stir well and let it sit for about 5 minutes to meld the flavors.

In a large mixing bowl, add diced cooked jumbo shrimp, chopped tomato, diced jalapeño (if using), and diced Hass avocado. Gently fold these ingredients together, ensuring the avocado stays intact.

Pour the dressing over the salad mixture. Gently toss to coat all ingredients without squishing the avocado.

Sprinkle freshly chopped cilantro over the salad and fold it in gently, ensuring all ingredients are well mixed.

Taste the salad, adjusting seasoning with additional salt and pepper if needed. Serve immediately or chill briefly for a refreshing touch.