Cook the brown rice: Rinse 1.5 cups brown rice under cold water until the water runs clear. Combine with 3 cups water and a pinch of salt in a pot.
Bring to a boil, reduce to low, cover, and simmer 35–40 minutes, or until tender. Fluff and keep covered.
Prep the sauce: In a bowl, whisk soy sauce, honey (or brown sugar), rice vinegar, sesame oil, and water. In a separate small bowl, stir cornstarch with 1–2 tablespoons water to make a slurry.
Set both aside.
Season the chicken: Pat chicken dry and season lightly with salt and pepper. Dry chicken browns better and holds sauce nicely.
Stir-fry the vegetables: Heat 1 teaspoon oil in a large skillet over medium-high. Add broccoli and bell pepper with a pinch of salt.
Cook 3–4 minutes until crisp-tender. Add carrots for the last minute. Transfer veggies to a plate.
Sear the chicken: Add 1 tablespoon oil to the same skillet.
Add chicken in an even layer. Cook without moving for 2–3 minutes to get color, then stir and cook another 3–4 minutes until nearly cooked through.
Add aromatics: Stir in garlic and ginger. Cook 30 seconds until fragrant, being careful not to burn.
Build the teriyaki: Pour in the sauce base and bring to a simmer.
Stir in the cornstarch slurry and cook 1–2 minutes, stirring, until the sauce thickens and turns glossy. If it gets too thick, add a splash of water.
Combine: Return the veggies to the pan and toss to coat. Taste and adjust with a little more soy for salt or honey for sweetness.
Assemble the bowls: Spoon brown rice into bowls.
Top with teriyaki chicken and veggies. Garnish with green onions, sesame seeds, and a drizzle of sriracha if you like heat.