On a cutting board, dice the cucumber into quarter-inch pieces – to peel or not to peel is up to you. Seed and dice the tomatoes into quarter-inch pieces. Combine the cucumber, tomatoes and half of the shallot or red onion in a bowl and reserve.
In a small bowl, whisk together the mustard, sugar and white wine vinegar and the remaining half of the shallots. Stream in the EVOO while continuing to whisk. Stir in the dill and season the dressing with salt and pepper, to taste.
Season the salmon with seafood seasoning and a little black pepper. Heat a nonstick skillet with a drizzle of EVOO over medium-high heat. Place the salmon rounded side down and cook until golden and a little crispy at the edges, 3-4 minutes. Flip and cook for 2 minutes more for a pink center, or 4 minutes for opaque fish.
Transfer the salmon to dinner or serving plates; top with the cucumber-tomato relish and cover with a liberal amount of dill dressing.