Heat the vegetable oil in a large skillet or wok over medium-high heat. Add the mixed vegetables and sauté for about 2-3 minutes until they are tender.
Push the vegetables to one side of the skillet and pour the beaten eggs into the other side. Scramble the eggs until fully cooked, then mix them with the vegetables.
Add the cooked chicken to the skillet and stir to combine with the vegetables and eggs. Cook for an additional 2 minutes.
Add the cooked rice to the skillet, breaking up any clumps. Pour in the soy sauce and teriyaki sauce, mixing everything thoroughly. Cook for another 3-4 minutes, allowing the rice to heat through and absorb the flavors.
Drizzle the sesame oil over the rice and add the chopped green onions. Stir well to combine. Season with salt and pepper to taste.
Serve hot, garnished with additional green onions if desired.