Preheat the oven to 425°. In a spice grinder, combine the sesame seeds, curry powder and crushed red pepper and pulse until coarsely ground. Season the salmon with salt and pepper, brush one side of the fillet with 1 tablespoon of the Dijon mustard and coat with the ground sesame seed mixture.
In a large, ovenproof, nonstick skillet, heat 1 tablespoon of the olive oil. Add the salmon, coated side down, and cook over moderately high heat until lightly browned, about 3 minutes. Carefully flip the salmon. Transfer the skillet to the oven and roast for about 10 minutes, until the salmon is just cooked through. Transfer the salmon to a cutting board.
In a large bowl, whisk the lemon juice with the remaining 1 teaspoon of mustard and 1 tablespoon of olive oil. Season the dressing with salt and pepper. Add the tomatoes, serrano chile and cilantro and toss. Cut the salmon into 4 pieces and serve right away with the tomato salad.