Fill a shallow wide pan with high sides with 1 inch of water and put over high heat. Add peppercorns, bay leaf and 1 section of lemon to the water and allow to come barely to a simmer. Place fish in the poaching liguid and cook, barely simmering, for 6-8 minutes, until flesh just begins to whiten all the way through. Usiong a wide spatula remove fish from the water and set aside to cool.
Empty the pan and return to the stove, over medium-high heat. Add butter, and allow to melt, swirling pan. When butter foams, ass the celery, onions and garlic and saute, stirring often, until veggies soften and onion turns translucent, then transfer to a large bowl.
In a small bowl, mix together the mayo, mustard, eggs, salt, pepper and Old Bay seasoning, then add this mixture to the veggies, pour the panko crumbs over them and stir to combine. Add cilantro and stir again.
Flake the cooked fish into the binding mixture carefully, keeping the flakes as whole as possible, then gather into small balls and form into patties, 4-6 form main course, 6-8 for appetizers. Place on a platter, cover loosely with pastic wrap and refrigerate for at least one hour to set up.
Set a large saute pan over high heat and add the grapeseed oil. When the oil shimmers, remove the cakes from fridge and spread both sides with mayonnaise and carefully sute until goldwen brown, about 4-5 minutes per side. Drain on paper towel and serve with remaining lemon wedges.