In a large soup pot, render the bacon fat over medium heat and cook until crisp. Remove bacon and set aside.
Add the diced onion and cook in the bacon fat until the onions are translucent and tender. Next, add the diced carrots and celery and cook in a pot for 5-7 minutes until tender.
Add the dried split peas to the pot and cook in the vegetables for a couple minutes—season with salt and pepper.
Add the vegetable or chicken stock to the pot and bring to a simmer. If you have a ham bone, add it to the pot and cook on a low simmer, occasionally stirring for 60-90 minutes or until the peas are tender.
Garnish with reserved crisp bacon pieces and sliced green onions.