In a medium bowl, combine together diced tomatoes, onion and lemon juice. Season with salt and pepper, to taste. Set aside.
Rub the salmon fillets on both sides with olive oil and then sprinkle with seasoning salt.
Place salmon in hot grill pan, and cook for 4 minutes, or until golden underneath.
Use a slotted spatula to turn salmon over, then cook the fillets for 2 to 3 more minutes, or until just cooked through.
Remove salmon from heat, let rest for 30 seconds and sprinkle with a good squeeze of lemon juice, if desired. Serve with the tomato salsa.