In a large bowl, gently combine the lump crab meat with panko, mayonnaise, egg, Dijon, Worcestershire, Old Bay, chopped parsley, sliced green onions, lemon zest, lemon juice, salt, and black pepper. Use a light hand so you don't break up the lumps of crab meat. Mix until ingredients are incorporated and mixture holds together when pressed. If mixture feels too loose, add up to 2 tablespoons more panko, 1 tablespoon at a time.

Form cakes

Divide the mixture into four equal portions (about 4 ounces each). With lightly oiled or wet hands, gently shape each portion into a 3–3.5-inch patty about 3/4-inch thick. Place on a parchment-lined tray and refrigerate for at least 30 minutes to firm, or up to 2 hours.

Cook crab cakes

Heat a large skillet over medium heat and add 1 tablespoon butter and 1 tablespoon neutral oil. When butter is foamy and oil shimmers, add crab cakes (work in batches if needed) and cook undisturbed until golden brown and crisp, about 3–4 minutes per side. Reduce heat slightly if they brown too quickly. Carefully flip and cook the second side until internal temperature is 145°F or cakes are heated through and golden, about another 3–4 minutes. Transfer to a paper-towel-lined plate and keep warm in a low oven (200°F) if needed. Add remaining 1 tablespoon butter to pan for second batch.

Sweet Chili Mayonnaise

Whisk together the mayonnaise, sweet chili sauce, sriracha (if using), lime juice, and a pinch of salt in a small bowl until smooth and homogeneous. Taste and adjust sweet-spice balance. Chill until assembly.

Southern Slaw

In a medium bowl, combine shredded green cabbage, red cabbage, and grated carrot. In a separate small bowl, whisk together mayonnaise, apple cider vinegar, brown sugar, Dijon, celery seed, salt, and pepper. Pour dressing over shredded vegetables and toss until evenly coated. Let sit at least 10 minutes to meld flavors; refrigerate if making ahead (up to 4 hours). Stir again before using.

Sandwich Assembly & Garnish

Toast buns: Spread softened butter on the cut faces of the brioche buns. Toast in a hot skillet or under a broiler until golden and crisp, about 1–2 minutes per side; watch closely.

Season tomato: Lightly salt and pepper tomato slices and set aside.

Assemble sandwiches: Spread about 1 to 1 1/2 tablespoons of the sweet chili mayonnaise on the bottom half of each toasted bun. Place 2 leaves of butter lettuce, then a slice of tomato. Set a warm crab cake on top of the tomato. Top the crab cake with 2-3 tablespoons of southern slaw (as desired) and an additional drizzle (about 1 teaspoon) of sweet chili mayonnaise if you like extra sauce. Cap with the top bun.

Serve: Serve immediately with lemon wedges on the side for squeezing over the crab cake. Optionally serve fries or chips as a side. Leftover components: store crab cakes refrigerated up to 2 days (reheat gently), slaw refrigerated up to 3 days, and mayo sauce refrigerated up to 4 days.