Reduce heat to medium and cook onion, bell peppers, and remaining 1 Tbsp. oil, stirring, until tender but not browned, 6–8 minutes; season with salt and black pepper. Add cumin, paprika, oregano, and cayenne and cook, stirring, until fragrant, about 1 minute. Add chicken stock and reserved beef along with any accumulated juices to pot. Stir in sugar, 4 tsp. salt, and ¼ tsp. black pepper. Bring to a simmer and cook, stirring and scraping up any brown bits, until most of the liquid is evaporated, 15–20 minutes; taste and season with salt and black pepper, if needed. Stir in raisins. Transfer to a medium bowl, cover, and chill at least 3 hours.