Heat the olive oil in a large pot over medium heat. Add the diced onion and cook until softened, about 5 minutes.
Add the minced garlic and cook for another minute until fragrant.
Stir in the diced carrots, celery, and bell pepper. Cook for about 5 minutes until the vegetables start to soften.
Add the chopped collard greens to the pot, stirring until they begin to wilt.
Pour in the vegetable or chicken broth and bring the soup to a simmer. Let it cook for about 15-20 minutes, or until the collard greens are tender.
Add the cooked black-eyed peas to the pot along with the smoked paprika, ground cumin, salt, pepper, and red pepper flakes if using. Stir well to combine.
Let the soup simmer for another 10-15 minutes to allow the flavors to meld together.
Taste the soup and adjust the seasoning as needed.
Serve the collard green and black-eyed pea soup hot, optionally with a squeeze of fresh lemon juice over each bowl.