Preheat the oven to 375 degrees F (190 degrees C). Lightly grease a 9x13 baking dish with cooking spray or butter.
Add imitation crab to a food processor and pulse 2 times to break it apart a bit. Reserve 2 tablespoons of the green onions and add remaining green onions to the food processor along with cream cheese, Sriracha, soy sauce, lemon juice, salt, and garlic powder; pulse a couple of times, just until everything is combined.
Place about 5 sheets of phyllo in the bottom of the prepared baking dish and brush with melted butter. Repeat twice and then place ½ of the crab mixture on top and spread evenly to the edges. Top with 5 more sheets of phyllo and coat lightly with butter.
Repeat once more and top with remaining crab mixture, spreading evenly over the top. Top with remaining phyllo (about 8 to 10 sheets) and pour over remaining melted butter.
Use a knife to make 3 vertical cuts all the way down to the bottom of the pan. Then make horizontal cuts, about 1 to 1 ½ inches apart, to create diamond shapes, being sure to cut all the way through.
Bake in the preheated oven until puffed and golden brown, 25 to 30 minutes. Let stand for 10 minutes before serving.
Just before serving, drizzle with sweet chili sauce or serve sauce on the side for dipping.
