In a large bowl, season the chicken with salt and pepper. Add the cornstarch and toss well to coat. In a medium bowl, crack the eggs and whisk to combine.
In a large skillet, heat the oil over medium heat. When the oil is hot, dip each piece of chicken into the egg and then add to the skillet.
Cook the chicken, turning a few times, until each piece is evenly golden brown and fully cooked, 7 to 9 minutes.
Make the sauce:
Meanwhile, melt the butter in a medium saucepan over medium heat. Add the garlic and sauté until fragrant, about 1 minute.
Add the sriracha, rice vinegar, brown sugar, sesame oil, crushed red-pepper flakes, and half of the scallions. Bring the mixture to a simmer, stirring constantly, and cook for 1 minute; remove from the heat.
When the chicken is done cooking, transfer it from the pan to a large bowl. Add the sauce, and toss well to combine.
Garnish with the sesame seeds and remaining scallions. Serve with the rice.