Make the sauce base: In a small bowl, whisk soy sauce, water or broth, brown sugar or honey, rice vinegar, and mirin.
Stir in the minced garlic and grated ginger. Set aside. In a separate bowl, mix cornstarch with equal parts water to make a slurry.
Heat the pan: Set a large skillet over medium-high heat.
Add the neutral oil and let it shimmer. A hot pan ensures good browning and flavor.
Cook the chicken: Add the ground chicken. Break it up with a spatula into small crumbles.
Season with a pinch of salt only if using low-sodium soy. Cook until no longer pink and lightly browned, about 5–7 minutes.
Add veggies (optional): If using quick-cooking vegetables, stir them in and sauté 2–3 minutes until crisp-tender.
Pour in the sauce: Give the sauce base a quick stir and add it to the skillet. Bring to a lively simmer so the flavors concentrate.
Thicken: Stir the cornstarch slurry again (it settles) and drizzle it into the pan while stirring.
Simmer 1–2 minutes, until glossy and slightly thick. If too thick, splash in a tablespoon of water; if too thin, simmer another minute.
Finish with sesame oil: Turn off the heat and stir in toasted sesame oil for aroma. Taste and adjust sweetness or salt if needed.
Garnish and serve: Top with sliced green onions and sesame seeds.
Spoon over warm rice or noodles, or tuck into lettuce cups.