To prepare ceviche:
Cut rockfish fillets into small cubes. Combine lemon and lime juice with rockfish in a large mixing bowl. Make sure fish is evenly coated with juice. Place in fridge and let sit for 15 minutes, stirring every 5 minutes to make sure fish is properly curing on all sides.
Afterwards, strain most of the juice, then add poblano, green chili, onion, tomato, cilantro, water chestnuts, garlic, olive oil, salt, sugar, and apple cider vinegar. Mix well and chill in fridge.
To prepare sauce:
In in a small mixing bowl, stir together yogurt, lime juice, cilantro, green onion, garlic, jalapeno, apple cider vinegar, avocado, salt, and pepper. Cover and chill in fridge.
Tip: You can mix the sauce in a blender or food processor for a creamier texture.
To prepare tortillas:
In a large mixing bowl, combine salt and masa harina. Slowly add small amounts of water and stir together. Knead dough for 2-3 minutes.
Cover with a damp paper towel and let rest for 10 minutes. Roll dough into 2 tbsp size balls. Flatten balls between 2 pieces of parchment paper or 2 zip lock baggies, making sure to roll dough out evenly into 5 inch tortillas.
Heat a nonstick pan, or cast-iron skillet, on medium to high heat. Cook tortillas, 1 minute on each side.
Take tortilla and top with spring mix, followed by thin slices of fresh avocado. Fill with ceviche and drizzle sauce over top. Plate with chopped cilantro and lime wedges. Serve immediately.