Heat a large 12-inch skillet over medium-high heat. Add the ground beef and crumble it with a meat chopper or sturdy spatula as it cooks. Add the green onions, garlic powder, salt, pepper, sriracha (if using), and soy sauce. Cook for 6-8 minutes, breaking up the meat continuously, until no pink remains and the beef reaches 160°F internal temperature with nice caramelized edges. If excess grease pools in the pan, carefully drain before transferring beef to a plate.

Keep the skillet on medium-high heat and add the avocado oil, letting it heat for 30 seconds. Add the shredded brussels sprouts and season generously with salt and pepper. Spread them in an even layer and resist stirring for 2-3 minutes to develop that golden-brown color on the bottom. Then stir and continue cooking for another 4-6 minutes until tender with crispy, caramelized edges throughout.

Return the cooked ground beef to the skillet along with the sweet chili sauce and fresh lime juice. Stir everything together for 1-2 minutes until the sauce coats all the ingredients evenly and everything is heated through. The sauce should be glossy and clinging to the beef and vegetables.

Remove from heat, sprinkle with sesame seeds if desired, and serve immediately. This dish is best enjoyed hot, when the brussels sprouts are still crispy and the sauce is at its most flavorful.