PLace the chicken breasts, garlic cloves, whole 1/4 onion, jalapenos, serranos and salt in a large stock pot. Fill with water until the breasts are covered.
Cook on medium high heat for 25-30 minutes or until chicken is tender and almost falling off the bone.
Take the chicken breasts out of the water and set aside.
Place the jalapenos, serranos, garlic, and whole onion in the blender. Add in 1/2 cup of the cooking liquid and blend on high for a minute or so until the chiles are pureed.
Heat the oil in a saute pan. While the oil is heating up, cut the zuchinni into a small dice about the size of sweet peas. Add the zuchinni and diced onion to the saute pan. Saute the mixture for 5 minutes or until the zuchinni starts to soften. Add in the 1/2 chicken bouillon cube and stir until it is melted. Pour in the chile and stir to combine. Let the mixture cook for 2 minutes on a low boil.
Next, shred the chicken using your fingers or two forks. Add the shredded chicken into the chile. Stir to combine. The mixture should not be too thick, if it is add an additional 1/4 cup of the cooking broth.
Taste for salt and add if necessary.
The mixture is now ready to be stuffed in tamales or whatever you may be using it for.