Combine the tuna, shallot, ginger, jalapeno (if using), sesame oil, soy sauce, and cilantro in a medium bowl and toss gently to combine. Cover with plastic wrap and refrigerate for 1 to 2 hours before serving.
Just before serving, fold in the avocado. Season with salt and pepper to taste. (I found that it was flavorful enough without salt and pepper, but season according to your taste.)
Serve with Bibb lettuce, to make lettuce wraps.
• For an appetizer, serve spoonfuls of the poke on rice crackers or toasted pita chips.
• Add diced mangoes to the tuna avocado mixture.
• Serve with a squeeze of lime juice.
• Substitute 2-3 tablespoons finely sliced green onions for the shallot.
• Sprinkle the poke with black sesame seeds.
• For a heartier meal, serve with brown rice in lieu of the lettuce.