Pour HamBeens 15-bean mix into large colander. Rinse beans in colander with running water, until water draining from beans runs clear.
Transfer rinsed beans to large bowl. Fill bowl with water to cover beans, then cover bowl with lid or plastic wrap. Set beans aside to soak 8 hours. See Notes for Quick-Soak Method.
Toward end of soak time, heat large pot on stovetop over medium heat. When pot is hot, add diced bacon to pot and cook until bacon is cooked through and crispy.
Transfer cooked bacon to bowl or plate and set aside. Do not drain rendered bacon fat from pot.
Add diced onion, minced garlic, and chopped celery to pot with bacon fat. Cook, stirring occasionally, until onion and celery are tender, approximately 3 to 5 minutes.
Add seasoning packet from dried soup, chili powder, salt, and freshly cracked black pepper to pot. Stir well to fully combine spices with veggies and rendered bacon fat.
Pour 6 cups chicken broth into pot and stir to incorporate spices, veggies, and liquid.
Drain water from bowl with beans, then add soaked beans to pot with chicken broth. Stir to incorporate, then let soup simmer, uncovered, 1 hour.
After soup has simmered 1 hour, add diced tomatoes and cooked bacon to pot and stir to incorporate. Cook soup, uncovered, 30 minutes more.
After 30 minute cook time, taste soup and adjust salt, pepper, and chili powder as needed. When satisfied with flavor, portion soup into serving bowls, top with shredded cheese and sliced green onions if desired, and serve warm.