Take the salmon out of the fridge and let it warm up on the counter for 15-20 minutes prior to starting the recipe if possible.
Meanwhile, add the slaw dressing ingredients (mayo, sour cream, sriracha, honey, lime juice, salt) to a fairly large prep bowl and mix together until smooth, then add in the shredded cabbage, scallions, and cilantro. Toss until coated. Taste and adjust as needed.
Season the salmon with the chili powder and salt & pepper.
Add the olive oil and butter to a skillet over medium-high heat. Once the pan is hot, add the salmon to the pan. Cook the salmon (skin-side down) for 5 minutes, then reduce the heat to medium and flip it over and cook for another 2-4 minutes or until it's cooked through (it'll take a little longer if your salmon is more than 1" thick, and less if thinner than 1" or skinless).
Break the salmon up into desired size pieces right in the skillet (peel off the skin first and discard it if you don't want to eat it). Serve with warmed tortillas, slaw, and avocado.