Heat a little bit of oil in a large pot over medium to medium-high heat. Add the onion cut-side down and cook until charred.
Add the vegetable stock, salt, garlic powder, black pepper, and red pepper flakes to the pot and bring to a boil.
Add the cut collard greens to the vegetable broth, cover, and let simmer until nice and silky, anywhere from 45 minutes to 2 hours (or more).
Add the vinegar, taste, and adjust the seasonings as you see fit. Serve.
