Brush the salmon with the olive oil and sprinkle the Old Bay Seasoning, garlic salt, cayenne pepper, salt and pepper over the salmon until evenly coated. Set aside.
To make the slaw, cut the peel and the white pith off of the grapefruit. Cut between the membranes to get the natural segments and then cut those into chunks. Place in a medium bowl and add the cabbage, cilantro, cucumber, garlic, and lime juice. Toss until combined.
To make the crema, add all the ingredients to a blender and blend until smooth.
When you are ready to make the fish, heat a grill (pan or outdoor grill) to medium high heat. Once the grill is hot add the fish skin side down, and sear for 3-4 minutes. Flip and grill for another 3-4 minutes. Remove the skin.
Chop the fish into pieces. Warm the tortillas and add fish, top with grapefruit slaw and drizzle avocado crema over the top. Enjoy!