Nutritional yeast is inactive yeast, often used for its savory, cheesy flavor. It's vegan and gluten-free and available in most health food stores. It's also got tons of nutrients, including B-vitamins, zinc and protein.*
Sometimes it's powdery, sometimes it's flaky, but it is always GLORIOUS.
*Check the label on the brand you're buying for specifics on nutritional info — not all nutritional yeasts are the same.