Transfer the lettuce, chickpeas, tomato, olives, olive brine, red onion, sun-dried tomatoes, oil (if using), and hemp hearts (if using) to a large cutting board with grooves. Use a large chef's knife to chop the ingredients until very finely chopped.
Add the hummus, lemon juice, sriracha, and oregano. Use a bench scraper to combine the ingredients until fully incorporated. Adjust salt, pepper, lemon juice, and sriracha to taste.
Transfer one-third of the mixed ingredients to one slice of toasted bread or flatbread.
