In one cup of the chicken stock, simmer the scallions, cilantro, and cumin for 5 minutes. Set it aside until it is cool, then process in a blender or food processor until you have a smooth, green-colored puree to be added to the final soup.
In the remaining 1 ¼ quarts of chicken stock, simmer the quartered, skinned chicken breasts. Skim off the scum that results and discard. The chicken will take about 1 hour to cook.
As the chicken is simmering, add the cut up, peeled yucca, and the cut up potatoes. Continue to skim off the scum after the yucca and potatoes are added.
30 minutes prior to the end of cooking, add the cut up plaintains.
10 minutes before completion of the cooking phase, add the processed scallions-cilantro-cumin mixture and the juice from the 2 lemons.
Combine the flour and the butter for the roux and microwave for 30 seconds. The result should be a yellowish sludge.