In a medium bowl, whisk together ¼ cup mayonnaise, 1 tablespoon sriracha, 1 teaspoon sesame oil, 1 tablespoon soy sauce, and the juice of half a lime until smooth and creamy. Gently fold in the diced sushi-grade tuna, 2 tablespoons of red onion, 2 tablespoons of chopped green onions, and 1 tablespoon of toasted sesame seeds. Cover and chill in the refrigerator for 20 minutes.

In a large skillet, heat about 1 cup of oil over medium heat until shimmering, approximately 350°F. Fry each wonton wrapper one at a time, pressing them gently into taco shapes using a mold or utensil until golden brown and crispy, approximately 1-2 minutes per side. For a healthier option, bake the wrappers at 375°F for 6-8 minutes, flipping halfway, until they're golden and crisp.

Once the wonton shells are ready, carefully remove them from the oil or oven and let them drain on paper towels. In each crispy taco shell, generously fill with the chilled spicy tuna tartare mixture. Be sure not to overfill to prevent spillage.

Top the filled tacos with sliced avocado and any desired garnishes, such as additional sesame seeds, chopped green onions, or jalapeños for an extra kick. Arrange the tacos on a vibrant serving platter and serve immediately.