For the salmon: In a saute pan over medium-high heat, add the oil and allow to warm. Next, sprinkle the salmon fillets with the salt and pepper. Then, add to the oil, skin-side up, and allow to sear for 3 to 4 minutes. Reduce the heat to medium, flip the fish and repeat cooking until desired temperature, 3 to 4 minutes. Once cooked, remove from the pan and allow to rest for 4 to 5 minutes before serving.
For the salad: In a saucepan over high heat, combine 2 cups water, the white balsamic vinegar and sugar. Stir the mixture and heat until the sugar is fully dissolved. Once the sugar is dissolved, add the onions and cook for 3 minutes. Then add the tomatoes and cook for a final minute. Once the tomatoes have cooked, remove from the heat and toss in the watermelon and basil. Portion to plate and finish with the seared salmon.