Season chicken with half the salt and brown lightly in oil. Transfer to a plate.
Cook yellow onions for 8 minutes. Add garlic, chile paste, cumin, and pepper and cook for 3 minutes.
Return chicken, add stock and remaining salt, and simmer covered for 45 minutes. Add peas and simmer uncovered 10 minutes until the sauce lightly coats the chicken.
Cook the Accompaniments:
Boil the potatoes in salted water until tender, about 20 minutes.
Steam the pre-soaked tunta until tender, then split and tuck a slice of queso fresco into each piece.
Make Sarza and Serve:
Toss red onion, tomato, parsley, and oil.
Arrange chicken with its yellow chile sauce, potatoes, stuffed tunta, and sarza on a warm platter.
Notes
Yellow chile paste varies in heat, so taste before adding more.
Refrigerate chicken and sauce for three days; store the sarza separately.