Heat a medium non-stick skillet over medium heat. Mix the olive oil and lemon juice in a bowl.
Season the salmon fillets with pepper and coat each side with the oil and lemon juice. Let them rest in the bowl until the pan is preheated.
Place salmon fillets in the pan skin side down. Cover the top and let them cook for 4-5 minutes until cooked throughout. For a pan-seared crust once they are finished, flip them over for a few seconds to brown the top.
In a large bowl toss together the arugula, tomatoes, onion, salt, pepper, olive oil, and vinegar.
Sprinkle the fish with fresh lemon and serve over the simple salad.