This vegan split pea soup recipe makes a very thick soup. To make it thinner, reduce the amount of split peas or add more water. Depending on the density of split peas, it may take a while for the vegetables and peas to soften, but you can't really overcook this soup; just stir occasionally and add water if it gets too dry. Seasonings can be altered to taste. This soup tastes even better reheated the next day.