Mix lemon juice, mustard, and garlic in a bowl. Whisk in the miso until is well combined. Slowly add the olive oil, whisking continuously, to make a mayonnaise. When the oil is fully integrated, mix in the yeast, salt and pepper. Taste it, and if it is too strong, dilute it by whisking in soymilk one tablespoon at a time.
Traditional caesar salads use raw egg to make a mayonnaise dressing. In this recipe, the miso replaces the egg. If you live somewhere where you can buy vegan worcestershire sauce or fake parmesan vegan cheese, they would both probably enhance the recipe.