In a large pot, warm 1 tablespoon oil over medium heat. Add the pork and ¼ teaspoon salt, then break into chunks. Cook for about 5 minutes, stirring halfway through, so that the pork gets nice and browned. Continue to break into smaller chunks and cook until cooked through and deeply browned. Use a slotted spoon or spatula to transfer the pork into a paper towel lined bowl or plate.
In the same pot over medium heat, add the onion, celery, and ½ teaspoon salt and cook until softened, about 5 minutes, scraping up any porky bits stuck to the bottom of the pot. Add the garlic, fennel seeds, oregano, and red pepper flakes (if using) and cook for 30 more seconds.
Stir in the sweet potatoes, water, beans, and remaining ½ teaspoon salt. Bring to a boil, then reduce heat to low and simmer for 15 minutes, stirring occasionally. Transfer about ½ cup of the broth to a small bowl. Add the miso paste and use a fork to mash/dissolve it.
Stir the greens and cooked sausage into the soup and simmer for 2 more minutes, or until greens are tender/wilted (you can also just top the soup with the browned pork instead of stirring it in). Remove from heat and stir in the miso water and lemon juice. Served topped with fresh herbs and drizzle with olive oil and some black pepper, if you’d like (recommended!).