Heat the olive oil. Sautee the leeks (or scallions) for about 2 minutes. Add the garlic, and sautee for another 30 seconds or so. Add mushrooms, and sautee until they are wilted and the liquid the mushrooms gave off has evaporated. (I don't mind the liquid, I actually think it works better with it in the end..) Then add the vinegar. Stir, season with a bit of salt, and set aside.
THEN, cook the angel hair pasta. (Allowing the veggie mixture to set while the pasta is cooking allows the flavor to enhance itself.) When pasta is ready, drain, and then add the veggie mixture, and viola, the best tasting pasta dish EVER!!