Heat 2 tablespoons of oil to medium heat. Add the onions, garlic and pickled jalapeños and cook for 3 to 4 minutes. In the blender, add the tomatoes, cumin, oregano, chile ancho powder, pepper, pinch of salt, chicken broth and brine from jalapeños. Blend on high until smooth, taste for salt.
Add the tomato mixture to the pan with onions. Bring to a boil, reduce heat, add chicken, peas and carrots. Cook at a low simmer until most of the broth reduces, about 20 minutes. Taste for salt and set aside.
Peel and wash the tomatillos. Transfer them to a pot and cover with water. Bring to a boil reduce heat and cook for 10 minutes. Drain and transfer them to blender. Add chile serrano, garlic, cilantro, cumin and 1 teaspoon of salt. Blend on high until smooth, set asid
Preheat oven to 350ºF. Add 1 cup of salsa verde to the bottom of a baking dish (9×13) and spread out evenly, set aside. Heat a large griddle pan to medium heat. Brush the corn tortillas with olive oil on both sides. Heat the tortillas for a minute per side or until you get some light golden spots. Stack the tortillas onto a plate as you heat them.
Fill each pepper with just enough chicken filling so it still closes, do not over-fill. Wrap one tortilla around each chile relleno as tight as you can and transfer them, seam-side down to the baking pan with salsa verde. Cover the enchiladas with just enough salsa verde to cover, add cheese and bake in preheated oven just until cheese melts. Garnish with any leftover salsa and any or all of the garnishes listed. Serve with your favorite rice.