Heat olive oil in a large pot over medium heat. Add onion, garlic, and red bell pepper. Cook for about five minutes, stirring often, until the vegetables are soft. Stir in cumin, chili powder, smoked paprika, and cayenne pepper if you want. Cook for one minute, stirring constantly, to lightly toast the spices.
Pour in chicken broth and diced tomatoes. Stir well, then bring the pot to a gentle boil. Stir in black beans, corn, and shredded chicken. Lower the heat and let the soup simmer for 15 minutes, stirring occasionally.
In a small bowl, whisk masa harina with water until smooth and lump-free. Slowly stir this mixture into the soup. Let the soup simmer for another 10 minutes. It should thicken slightly and coat the back of a spoon.
Stir in heavy cream and let the soup warm for two more minutes. Taste and add salt and pepper if needed. Ladle the soup into bowls. Top each bowl with crispy tortilla strips, shredded cheese, avocado, cilantro, and a squeeze of lime.