Heat the butter in a medium skillet set over medium heat until melted. Add the onion, bell pepper and garlic. Cook, stirring occasionally, until the vegetables are soft, about 3 to 4 minutes. Add the cumin and season with salt and pepper. Remove the skillet from the heat and transfer the vegetables to a large bowl.
Meanwhile, place the cooked chicken in the bowl of a food processor or a meat grinder. Process for a couple of minutes until very finely chopped, or pass through the ginder, and then add to the onion mixture.
In a small bowl, combine 1/2 cup of the bread crumbs with the eggs and chicken broth. Mix well and then add to the chicken and vegetable mixture. Place the rest of the bread crumbs in separate bowl. Line a baking sheet with parchment paper.
Divide the chicken mixture into about 20 small balls. Roll each croquette in the bread crumbs until coated. Set the croquettes on the prepared sheet. Place in the fridge to rest for about 3 hours.
In a fry pan over medium-high heat, pour in the oil, enough to cover the croquettes, and heat to 350°F. Using tongs, carefully place 3 or 4 croquettes in the hot oil (do not crowd the pan) and cook, turning as needed, until golden brown, about 4 minutes. Repeat with the remaining croquettes.