Spicy Tuna Lettuce Boats

Mix together the drained tuna, finely chopped celery, finely chopped red or white onion, mustard, mashed avocado, olive oil, and salt and pepper to taste. If desired, add optional flavor enhancements like a squeeze of lemon, a pinch of chili flakes, a splash of apple cider vinegar, or chopped pickles or capers. Scoop the prepared tuna mixture into long romaine lettuce leaves. For a carb-rich alternative, serve the mixture on sourdough bread as a sandwich.