Add the water, honey, rice vinegar, soy sauce, ginger, garlic and red pepper flakes to a small-pot.
Heat on medium-high, stir till smooth and bring to boil. Add in cornstarch-slurry and stir constantly till the sauce thickens for a few minutes.
Heat 1/2 tbsp oil in a large saute pan or wok over medium-high-heat. When the oil is hot, but not smoking, add the chicken along with a few dashes of soy-sauce.
Cook the chicken till it is fully cooked through and golden-brown on all sides, for 4-6 minutes. Use a large spoon to transfer the chicken to a plate and put aside.
Heat the remaining ½ tbsp oil. Then add the bell peppers and asparagus and let cook for 3-4 minutes or till softened and lightly browned.
Once the vegetables are done, add the water chestnuts to the pan and then return the chicken to it. Pour in the sauce and toss to coat. Allow the chicken to simmer for a few minutes to warm the chicken. Mix in half the green onions.
Sprinkle the remaining green onions and sesame seeds over the top. Serve warm with red pepper flakes or soy sauce if desired.