Put the chicken or hen with the whole scallions, onion and cilantro in a large pot with the water. Cover and cook over high heat until boiling then reduce to low and simmer until cooked through and tender, 20 to 25 minutes for chicken or 45 minutes if using a hen. Remove the chicken from the pot and set aside. Remove whole scallions and onion and discard. Reserve the stock.
While the chicken cooks, prepare the sofrito. In a heavy skillet, heat the olive oil over medium to low heat and add all the ingredients for sofrito but the saffron. Saute the sofrito until very tender and paste-like, about 10 minutes. Add chicken pieces to sofrito and mix well continuing to saute for another 5 minutes.
Meanwhile, bring the stock to a simmer. Add the plantains and cook for 10 minutes. Then add the yucca, potatoes, corn, 1/4 cup chopped cilantro, and chicken cubes and simmer for another 10 minutes, orr until all the vegetables are tender when pierced. Add sofrito mix with chicken to the broth. Mix well. Simmer for another 5 minutes and remove from heat. Season with salt and pepper.
Before serving, garnish with chopped cilantro. Serve with avocado slices.