Allow tilapia fillets to thaw out fully before cooking. Lay fillets on sheet pan lined with enough parchment paper to completely wrap them.
Evenly distribute chopped cilantro, lime juice, 3 tablespoons of tomatillo sauce and olive oil over each fillet. Season each fillet with pinch of salt and pepper and wrap fillets in parchment paper, so they are completely sealed. Bake for 12 - 15 minutes at 350ºF. Fillets will steam in parchment paper to keep from drying out.
While fillets are cooking, combine julienned tomatillos, serrano pepper, red onion and cabbage. Make slaw dressing by combining mayonesa, smoked paprika, and salt together. Toss dressing with cabbage and tomatillo mixture and allow to sit in fridge 30 minutes before using to allow flavors to meld. Season to taste with more salt and pepper if needed.
Once fillets are cooked transfer them and all leftover liquid (very flavorful) to bowl. Shred fish with fork and mix it with all juices. Serve inside the bolillos or torta rolls and top with tomatillo slaw.