Wash and slice all your veggies and the chicken. Take out all sauce ingredients, and mix the cornstarch with the liquid.
If using hard veggies - Bring a pot of water to a rolling boil, add in some salt, and then your hard veggies (green papaya, carrots if cut thick, baby corn if you like them soft). Boil for a couple minutes until just softened (raw papaya takes about 3-4 minutes). Strain it and spread out on a plate to cool, or immediately put into a bowl of ice cold water to keep them crisp.
Heat your pan on medium high. Add in the oil, garlic, and onions. Fry until the garlic starts to brown a little. Then scoop everything out of the pan, leaving the oil.
Add in a bit more oil if needed, the chicken pieces, and some salt and pepper. Fry for a few minutes until all the pieces are browned, then scoop it out of the pan.
Then throw in the rest of your veggies. Starting with the hardest ones. Stir fry for a couple minutes until they soften a little but don't brown them too much.
Then add in all of your sauce ingredients, the pre boiled veggies, chicken, onion, and garlic.
Let everything come up to a simmer and cook for a few minutes until the sauce thickens and the veggies are soft to your liking. Do not overcook the veggies.
Taste and adjust salt/sugar/pepper/msg if needed, and take it off the heat.