Brown the sausage: Heat olive oil in a large pot over medium heat and cook the sliced sausage until the edges turn golden, about 5 minutes. Remove with a slotted spoon and set aside.
Soften the aromatics: In the same pot, add the onion and cook until translucent, about 4 minutes. Stir in the garlic and cook for 30 seconds until fragrant.
Build the broth: Pour in the chicken broth and stir in the Cajun seasoning, smoked paprika, and the soy sauce with rice vinegar. Bring the mixture to a gentle simmer.
Add the collard greens: Stir in the chopped collard greens since they take the longest to soften. Let them simmer uncovered for about 10 minutes.
Add kale and beans: Stir in the kale, white beans, and the reserved sausage. Simmer for another 8 to 10 minutes until the greens are tender but still have some bite.
Wilt in the spinach: Add the fresh spinach and stir just until it wilts into the broth, about 2 minutes.
Stir in the rice: Add the cooked rice and stir to combine, letting it warm through for 1 to 2 minutes.
Season and brighten: Taste the soup and adjust salt and pepper as needed. Finish with a tablespoon of lemon juice to brighten the broth.
Rest before serving: Let the soup sit off the heat for 5 minutes so the flavors settle before ladling it into bowls.