Thaw salmon, if frozen. Rinse salmon; pat dry with paper towels. Cut salmon into 1-inch chunks. Place salmon in a food processor. Cover and pulse with several on/off turns just until coarsely ground (do not overprocess); set aside.
In a large bowl combine panko, green onions, cilantro, ginger, and garlic. Stir in eggs, soy sauce, and lemon juice. Stir in salmon.
Line a baking sheet with parchment paper or foil. Divide salmon into four (about 2/3-cup) mounds on the tray. Shape each mound into a 1-inch-thick patty. Cover with plastic wrap; chill for at least 30 minutes or up to 8 hours (mixture will be easier to handle after chilling).
In a large skillet heat oil over medium-high heat. Add salmon patties. Cook for 8 to 10 minutes or until cooked through (160 degrees F), turning once halfway through cooking. Serve with Lime Mayonnaise. If desired, serve on buns with spinach and red onion.
In a bowl stir together mayonnaise, red onion, and lime juice. Refrigerate until ready to serve.