Make the crema: In a blender or food processor, combine Greek yogurt, lime juice, avocado, cilantro, jalapeño, olive oil, salt, and pepper. Blend until smooth. Add a little water at a time until it reaches a drizzle-able consistency. Set aside.
Cook the salmon: Heat a pan over medium-high heat with a little oil. Sear the salmon for about 3–4 minutes per side, or until cooked through and flaky. Remove and break into large chunks.
Warm the tortillas: Heat tortillas in a dry pan or directly over a flame until warm and slightly charred.
Assemble the tacos: Layer tortillas with sliced cabbage, salmon, and a generous drizzle of cilantro lime crema.
Finish and serve: Top with fresh cilantro, a squeeze of lime, and crumbled cotija cheese. Serve immediately.