In a large bowl, combine the lump crab meat, stone-ground mustard, mayonnaise, Worcestershire sauce, Old Bay seasoning, green onions, bread crumbs, beaten egg, salt, and black pepper. Gently mix until all ingredients are well combined, being careful not to break up the crab meat too much.

Form the Crab Cakes

Using your hands, form the mixture into patties, about 3 inches in diameter. Place the formed crab cakes on a baking sheet lined with parchment paper. Refrigerate for at least 30 minutes to help them hold their shape.

Cook the Crab Cakes

In a large skillet, heat canola oil over medium heat. Once hot, carefully add the crab cakes to the skillet. Cook for about 4-5 minutes on each side or until golden brown and crispy. Remove from the skillet and place on paper towels to drain excess oil.

Prepare the Tomato Salad

In a bowl, combine the diced tomatoes, olive oil, lemon juice, salt, and black pepper. Toss gently to combine.

Serve

On a plate, place a handful of watercress. Top with the crab cakes and serve alongside the tomato salad.