Dissolve 2 tablespoons kosher salt in 4 cups cold water to create a brine solution. Submerge chicken breasts completely and refrigerate for 15-30 minutes.
Remove chicken from brine, rinse thoroughly, and pat completely dry with paper towels. Pound thicker portions to ensure uniform 3/4-inch thickness throughout.
Heat 2 tablespoons oil in skillet over medium-high heat until shimmering. Season chicken with 1 teaspoon garlic powder, 1/2 tablespoon mixed herbs, and black pepper.
Place chicken in pan without overcrowding (work in batches if necessary). Sear undisturbed for 5-7 minutes on first side until golden brown.
Flip once and cook until internal temperature reaches precisely 165°F (73.9°C). Rest for 10 minutes before slicing.
Rinse rice in cold water until water runs clear. Combine rice with 4 cups broth in saucepan. Add 1/2 teaspoon salt, 1 teaspoon garlic powder, and 1/2 tablespoon dried herbs.
Bring to boil, then immediately reduce heat to lowest setting. Cover and simmer for 15-18 minutes until liquid is fully absorbed.
Remove rice from heat and let stand, covered, for 5-10 minutes. Fluff with fork before cooling.
If using vegetables, heat remaining tablespoon oil in skillet over medium heat. Sauté onions for 3-4 minutes, add garlic and cook for 30 seconds, add bell peppers and cook for 2 minutes, then add frozen vegetables and cook for 3-4 minutes.
Spread rice in thin layer on baking sheet to accelerate cooling. Slice chicken into 1/2-inch strips against the grain.
Allow all components to cool to room temperature (below 70°F) within 2 hours before packaging.
Portion approximately 1 cup cooked rice, 4-5 oz sliced chicken, and 1/2 cup vegetable mixture into each container. Seal containers and refrigerate immediately.