The most common way to cook leafy vegetables in most of southern and southeastern China is probably stir frying, so I'm afraid it's just the liquid left from stir frying (for some reason, the liquid might have been thickened using starch, but that's not very common). It could also be Chinese broth, which wouldn't taste chickeny because the main ingredients ...
None of the flavors were overpowering (it didn't taste mostly like onions or jalapenos or garlic)
That statement provides the key you can work with:
prepare a bowl of each ingredient.
make a reasonable guess as to the proportions and mix a sample from a small amount of each.
taste the sample:
if one ingredient is very overpowering, discard the sample and ...
First, ask if they cook any of the ingredients.
It's likely that they are all raw.
Next, I would probably start with a mix with an approximate base that has the same color as the original sauce ( e.g. 1:1:1 with one clove of garlic).
Save some of it on the side to use again, then add some of each ingredient to your base. 2:1:1:1 / 1:2:1:1 / 1:1:2:1 etc....