Dice the chicken breast into small, bite-sized pieces.
Heat the sesame oil in a large skillet or wok over medium-high heat.
Add the chicken to the skillet, season with sea salt and black pepper, and sauté until golden brown and cooked through.
Remove the chicken from the pan and set it aside on a plate.
In the same skillet, add the diced white onion, minced garlic, and grated ginger, cooking for 2 minutes until fragrant.
Stir in the mixed frozen vegetables, cooking until they are tender and heated through.
Push the vegetables to the side of the pan and crack the egg into the open space, scrambling it until fully set.
Return the chicken to the pan along with the cooked brown rice.
Pour the tamari over the mixture and stir-fry for 3 to 4 minutes until the rice is hot and well-coated.
Garnish with sliced green onions before serving.