Dice the chicken breast into small, uniform bite-sized pieces and season with sea salt and black pepper.
Heat the avocado oil in a large cast-iron skillet or wok over medium-high heat until shimmering.
Add the chicken to the skillet and sauté for 5-6 minutes until golden brown and cooked through, then remove from the pan and set aside.
In the same skillet, whisk the egg and scramble quickly until just set, then remove and place with the chicken.
Add the diced white onion to the skillet and sauté for 2 minutes, then stir in the minced garlic, grated ginger, and the frozen peas and carrots.
Add the chilled cooked brown rice to the skillet, spreading it out in an even layer to let it crisp and toast for about 2 minutes without stirring.
Return the chicken and egg to the skillet, then drizzle with coconut aminos and toasted sesame oil.
Toss everything together for another minute until the flavors are well combined and the dish is piping hot.
Garnish with thinly sliced green onions and serve immediately.