In a blender combine avocado, cilantro, buttermilk, lime juice, garlic, and salt. Blend until completely smooth. If needed, add a little more buttermilk to obtain a thick but pourable consistency. Set aside.
In a food processor combine about ¼ of the salmon, breadcrumbs, cumin, oregano, salt, and cayenne. Process until mixture forms a smooth paste. Add remaining salmon, jalapeños, cilantro, and green onion. Pulse until salmon and vegetables are finely chopped but not a paste.
Form salmon mixture into 4 patties.
In a large nonstick skillet heat oil over medium heat. Add burgers and cook, flipping once, until browned and cooked through, 8-10 minutes (internal temperature should reach 145℉).
Serve burgers on buns, topped with avocado ranch and lettuce.