Place 1 14-ounce package smoked kielbasa on cutting board. Using sharp knife, cut sausage in half length-wise. Place sausage halves cut-side down on cutting board, then cut each sausage half vertically, creating ½-inch-thick half-moon shaped pieces of sausage. Set aside.
Place large pot on stovetop over medium heat. When pot is warm, add 1 tablespoon vegetable oil. Swirl or tilt pot to distribute oil across entire surface, then continue heating pot until oil is hot and shimmery.
When oil is ready, add pieces of kielbasa and 1 medium yellow onion (chopped) to pot. Stir to incorporate, then sauté sausage and onions until sausage pieces are slightly browned and onions have softened, approximately 3 to 5 minutes.
Add 4 cloves garlic (minced) to pot and stir to incorporate. Sauté until garlic is fragrant, approximately 1 minute.
Add 6 cups low-sodium chicken broth to pot and stir to incorporate, scraping up any browned bits of onion or garlic that may have stuck to bottom of pot.
Add 1 1.4-ounce package dry vegetable soup mix, 1 14.5-ounce can black-eyed peas, 1 14.5-ounce can great northern beans, 1 27-ounce can turnip greens, 1 teaspoon hot sauce (optional), 1 teaspoon creole seasoning, salt, and freshly ground black pepper. Stir to fully incorporate all ingredients.
Increase heat under pot to medium-high and bring liquid to boil. Once boiling, immediately reduce heat to low and cover pot with lid. Let soup simmer, covered, 1 hour.
After 1 hour, remove lid and set aside. Stir soup, then taste and add more hot sauce, creole seasoning, pepper, and/or salt as desired. Stir to incorporate any additions.
When satisfied with flavor of soup, portion soup into serving bowls and serve warm.