Cook your base. Prepare rice according to package directions.
Fluff and keep warm. This gives you a head start while the turkey cooks.
Whisk the sauce. In a small bowl, stir together soy sauce, water, brown sugar, rice vinegar, sesame oil, and sriracha if using. Set aside.
In a separate cup, mix cornstarch with cold water until smooth.
Sauté aromatics. Heat oil in a large skillet over medium-high. Add onion and the white parts of the green onions. Cook 2–3 minutes until softened.
Add garlic and ginger; cook 30 seconds until fragrant.
Brown the turkey. Add ground turkey, breaking it up with a spatula. Cook 5–7 minutes until no longer pink. Season lightly with salt and pepper if desired.
Drain any excess liquid for a better sear.
Add vegetables. Stir in your mixed veggies. Cook 3–5 minutes until crisp-tender. Softer veggies (like bell peppers) take less time; denser veggies (like broccoli) may need an extra minute and a splash of water.
Pour in the sauce. Give the sauce a quick stir, then pour it into the skillet.
Bring to a gentle simmer.
Thicken. Stir the cornstarch slurry and drizzle it into the pan while stirring. Simmer 1–2 minutes until the sauce turns glossy and clings to the turkey and veggies. If it gets too thick, add a splash of water.
Taste and adjust. Add more soy for saltiness, brown sugar for sweetness, or vinegar for brightness.
Fold in the green onion tops.
Assemble the bowls. Spoon rice into bowls, top with the teriyaki turkey mixture, and sprinkle with sesame seeds. Serve hot.