Prepare chicken. Combine soy sauce, hoisin, rice vinegar, sake, and mirin in a medium bowl. Toss the chicken with 1 egg white and 1 tablespoon of sauce, reserving the remaining sauce. Let the chicken sit for 10 minutes.
Heat enough oil in a large saute pan over medium-high to come ½-inch up the sides. Coat chicken in cornstarch, shaking off the excess. Carefully lay chicken in the pan and cook until golden brown on both sides. Remove chicken and drain excess oil on paper towels.
Drain all but 1 tablespoon of the oil. Add sliced onion and saute for 4-5 minutes or until softened. Add ginger, garlic, and Thai chile and saute for 30 more seconds. Add reserved sauce, sugar, and chicken stock. Reduce heat to low and simmer for 2 minutes.
Add chicken back to the pan, spreading the chicken in an even layer. Beat eggs and egg yolk together in a medium bowl and pour the eggs into the pan over the chicken in a circular motion. Continue to simmer on low heat until the eggs have set.
Remove General Tso's chicken oyakodon from heat and serve on rice. Garnish with chopped scallions and sesame seeds. Serve immediately.
Notes
You can marinate the chicken for up to 30 minutes if desired.