Heat the toasted sesame oil in a large non-stick skillet or wok over medium-high heat.
Season the diced chicken breast with sea salt and black pepper, then add it to the skillet and sauté until golden brown and cooked through.
Push the chicken to the outer edges of the pan and add the white onion, carrots, garlic, and ginger to the center, stir-frying for 3 minutes.
Stir in the frozen peas and continue to cook until they are bright green and tender.
Push all ingredients to the side, crack the egg into the empty space, and scramble until fully set before mixing into the rest of the dish.
Add the chilled cooked brown rice and tamari to the pan, tossing vigorously for 2 minutes to ensure the rice is heated through and slightly crisp.
Remove from heat, garnish with sliced green onions, and serve immediately.