Mix the blackening spice. In a small bowl, combine 1 teaspoon paprika, 1 teaspoon smoked paprika, 1 teaspoon garlic powder, 1/2 teaspoon onion powder, 1/2 teaspoon dried oregano, 1/2 teaspoon dried thyme, 1/4 to 1/2 teaspoon cayenne (to taste), 1 teaspoon kosher salt, and 1/2 teaspoon black pepper. Stir well.
Prep the salmon. Pat salmon strips dry with paper towels. Drizzle with 1 tablespoon avocado oil and coat evenly.
Sprinkle the spice mix on all sides and press lightly to adhere.
Make the slaw. In a bowl, toss 3 cups shredded cabbage with 2 tablespoons lime juice, 1 tablespoon olive oil, a pinch of salt, and a handful of chopped cilantro. Set aside to lightly wilt.
Stir together the lime crema. Mix 1/2 cup sour cream (or Greek yogurt) with 1 teaspoon lime zest, 1 to 2 tablespoons lime juice, 1 small grated garlic clove, a pinch of salt, and 1 tablespoon mayo if you want it richer. Thin with a teaspoon of water if needed for drizzling.
Cook the salmon. Heat a large cast-iron or nonstick skillet over medium-high.
Add 1 to 2 tablespoons avocado oil. When shimmering, place salmon strips in a single layer. Cook 2 to 3 minutes per side until the crust is darkened and the fish flakes but stays moist.
Remove to a plate to rest.
Make cheese taco shells (if using). Heat a nonstick pan over medium. Sprinkle 1/3 cup shredded cheese into a 5- to 6-inch circle. Cook until bubbly and edges are lacy, about 2 to 3 minutes.
Let cool 30 seconds, then drape over a wooden spoon balanced on two cups to form a shell. Let set. Repeat for 6 to 8 shells.
For a faster route, bake cheese mounds on a parchment-lined sheet at 375°F for 5 to 7 minutes, then shape.
Prep lettuce wraps (if using). Separate large romaine or butter lettuce leaves, rinse, and pat dry. Stack two leaves for each taco if you want extra stability.
Assemble the tacos. Add a layer of cabbage slaw to each shell or wrap. Top with 2 to 3 pieces of salmon.
Add avocado slices, jalapeño, and radishes. Drizzle with lime crema and garnish with cilantro and green onions. Finish with a squeeze of lime.
Serve. Plate with extra lime wedges and hot sauce.
Enjoy immediately while the salmon is warm and the shells are crisp.