Open a can of chicken broth (many canned organic chicken broths have 0 carbs. Some canned chicken broths have 1 carb gram).
Add approximately 1/4 cup of vinegar (regular white vinegar has fewer carbohydrates than rice vinegar), and about 1/8 cup of soy sauce.
For the "hot", add about a tablespoon of Chinese dried hot chili (not the same as red pepperflakes or cayenne pepper. The texture of the dried Chinese chili is somewhere in between flakes and powder.
Heat the above broth. It makes great base for lots of additions. I add some of the following:
minced fresh ginger
minced fresh garlic
sliced mushrooms
julienned snow peas
chopped scallions
little bits of leftover tofu, shrimp, pork, and/or chicken
beaten eggs
bamboo shoots
spinach
bok choy
anything else that comes to mind
No corn starch is necessary. If you add beaten eggs to the broth, it will thicken quite nicely.