Heat 1 tbsp olive oil in a skillet over medium-high heat for about 60 seconds. Add your diced onion and cook for 2 minutes until it starts getting soft and slightly translucent. Then add minced garlic and stir constantly for 30 seconds—you want it fragrant but not brown. This step takes less than 5 minutes total and completely changes your soup's flavor profile.
Sprinkle in the cumin, chili powder, and smoked paprika while the garlic's still warm. Stir constantly for 45 seconds so the spices bloom and release their oils into the oil itself. You'll hear a gentle sizzle as the spices hit the heat—that's exactly what you want. Don't skip this blooming step or your spices stay bitter and flat.
Pour this whole mixture (oil, onions, garlic, and spices) into your slow cooker. Add the chicken breast, broth, water, diced tomatoes with their juice, and salt and black pepper. Stir everything together so the chicken's coated and the spices are distributed throughout. Set your slow cooker to low and cover it.
Let this cook on low for 4 hours without lifting the lid. I know it's tempting to peek, but every time you open it, you're releasing heat and adding 15 minutes to your cooking time. After 4 hours, carefully remove the chicken breast and shred it using two forks—it should pull apart almost effortlessly if it's cooked through.
Return the shredded chicken to the slow cooker. Add the frozen corn and drained black beans, then stir everything together. Let it cook for another 2 hours on low. This gives the beans and corn time to warm through and absorb the broth flavor instead of staying cold and separate.
After the final 2 hours, when your kitchen smells like warm cumin and caramelized onions, taste the soup and adjust seasonings as needed. You might want a pinch more salt or a squeeze of lime juice for brightness. This is your moment to make it exactly how you like it, so don't skip tasting and adjusting.
Ladle the soup into bowls and top with shredded cheddar cheese, fresh cilantro, a squeeze of lime juice, and crushed tortilla strips if you've got them. The cheese melts into the hot broth almost instantly, creating this creamy richness that wasn't there before. Serve immediately while it's piping hot.