Bring chicken, water or broth, and salt to a boil, reduce heat and simmer for 30 minutes, skimming the foam from the surface while cooking.
Remove the chicken and set aside in a bowl. Strain the broth and reserve the liquid, discarding any solids.
Bring a dry cast iron skillet or comal to a medium-high temperature. Add the pumpkin seeds and then sesame seeds toasting them until light brown. Stir while they're toasting so they don't burn.
Grind the seeds in a spice or coffee grinder or in a blender/food processor until very fine.
Add the pepitoria (ground seeds), cooked tomatillos, soaked and shredded corn tortillas, cilantro, mint, scallions and jalapeño pepper to a food processor. Add one cup of broth and process until silky smooth.
Return the chicken to the cooking pot. Pour the green sauce in the food processor over the chicken and add remaining 3 cups of water, stirring to mix well.
Simmer for 20 more minutes. Adjust seasoning and then serve.