Heat the oil in a dutch oven or large pot over medium-high heat.
Add the onion, celery, and garlic to the pot and cook, stirring often, until the vegetables soften a bit, about 5 minutes.
Stir in the split peas, soy sauce, water, thyme, and bay leaves and bring to a boil.
Place a lid on the pot then reduce the heat to medium-low and simmer the soup, stirring occasionally, until the peas are just tender, about 45 minutes.
Stir in the carrots, potatoes, 1 tsp salt, and ¼ tsp black pepper then return to a boil over medium-high heat.
When the soup begins to boil again put the lid back on the pot and reduce the heat to medium-low then continue to simmer the soup until the potatoes and carrots are tender, about 20 more minutes.
Season the soup with additional salt & pepper to taste.
