In a small bowl, combine 1 teaspoon ground cumin, 1 teaspoon garlic powder, 1/2 teaspoon dried thyme, 1/2 teaspoon kosher salt, and 1/2 teaspoon ground black pepper. Rub this spice mixture evenly over both ribeye steaks.
Place the seasoned steaks into a zip-top bag and refrigerate to marinate for at least 1 hour or up to overnight. If short on time, you may cook them immediately after rubbing.
When ready to cook, heat a skillet or grill pan over medium heat until hot.
Remove the steaks from the bag and place them in the hot skillet or on the grill pan. Sear the steaks 3–5 minutes per side, until a crust develops and they reach your desired doneness. Transfer the steaks to a plate and let them rest while you make the soup.
With the same skillet (use the pan juices left from the steaks), add the 1/2 onion, chopped, and sauté over medium heat until translucent, about 3 minutes. Remove the onion from the skillet and set aside.
Pour the contents of both 15-ounce cans of black beans into a medium saucepan over medium heat. Add the sautéed onion, the 2 cloves garlic (chopped), and 1 cup beef stock.
Bring the bean mixture to a gentle simmer and cook, uncovered, for about 10 minutes to heat through and meld flavors. Stir occasionally.
While the soup is simmering or immediately after, slice the rested steaks into thin slices or bite-sized pieces.
Add the sliced steak to the soup, stir to combine, and heat for 1–2 minutes more to warm the steak through.
Ladle the soup into bowls and serve warm.