Heat 2 tablespoons oil in a large skillet over medium-high heat until shimmering.
Add the cubed chicken, season with salt and pepper, and cook until no longer pink in the center, about 4–6 minutes, stirring occasionally.
Add the diced onion, bell pepper, frozen peas and carrots, and minced garlic; sauté for about 1 minute until vegetables begin to soften.
Stir in the cooked brown rice and 3 tablespoons low-sodium soy sauce, then stir-fry for 2–3 minutes until everything is heated through and well combined.
Remove from heat and let cool for 5 minutes, then divide into 4 meal-prep containers. Drizzle with sriracha if desired.
Allow to cool completely before refrigerating or freezing.
