Combine all ingredients for the marinade in a bowl and mix well. Place steak in a plastic storage bag, add the marinade, remove as much air as possible and refrigerate overnight. Preheat grill pan over medium-high heat. Remove steak from marinade bag and remove as much of the marinade as possible. Reserve 1/2 cup marinade for barbeque sauce. Season the steak with kosher salt and pepper. Brush grill pan lightly with canola oil, grill steak for 2 1/2 minutes, rotate on same side 45 degrees (to create grill marks) and grill for another 2 1/2 minutes. Flip steak and cook for an additional 5 minutes on the other side, rotating 45 degrees after 2 1/2 minutes. Remove from grill pan and allow the steak to rest for 10 minutes under a foil tent. Slice steak against the grain as thinly as possible. To serve, toss salad and optional red onion, tomato and avocado with vinaigrette of your choice and arrange on a serving platter. Place a heap of fennel slaw in the center of salad, then place sliced meat around the sides (I fold the sliced meat in a slight V shape to show as much of the caramelization of the outside of the meat). Drizzle meat with barbeque sauce and mango puree carefully ensuring that the sauce gets onto the salad greens and slaw (use more barbeque sauce than mango puree).
Puree mangos in a blender. Add rice wine vinegar and chili garlic paste and blend until all ingredients are incorporated (the color should be a bright orange-red). Bring marinade to a boil. Lower heat to medium-low and reduce to about half (about 10 minutes over medium-low heat). The sauce can be strained at this point to remove the bits of garlic and ginger (the flavor is slightly less intense but it makes for a nicer presentation). Add about half of the mango puree (approximately 2/3 cup) and cook for another 2 minutes. Set aside. Save the other half of the mango puree for garnish.
Place lemon juice in a bowl and whisk in olive oil to create an emulsion. Add honey, zest, salt and pepper and whisk until combined; set aside. Slice fennel very thinly with a mandolin. Combine fennel and dressing and set aside until ready to serve. Re-season with salt and pepper, to taste, and sprinkle with black sesame