Grilled salmon and smokey tomato-chipotle sauce

For the sauce:
2 tablespoons extra-virgin olive oil
1/2 cup finely chopped red onion
2 teaspoons minced garlic
1 teaspoon dried oregano
1 can (28 ounces) whole tomatoes
1 chipotle chile in adobo sauce
1/2 teaspoon granulated sugar
1/2 teaspoon kosher salt
1/4 teaspoon finely chopped black pepper
4 salmon fillets (with skin), 6 to 8 ounces each and about 1 inch thick
Extra-virgin olive oil
Kosher salt
Freshly ground black pepper

1. To prepare the sauce: In a medium saucepan, warm the olive oil over medium-high heat. Add the onions and cook until soft, 4 to 5 minutes, stirring occasionally. Add the garlic and oregano, and cook until the garlic is light brown, about 1 minute, stirring occasionally. Add the tomatoes (including the juice) and the chile. Season with the sugar, salt, and pepper. Bring the sauce to a boil, then lower heat to a simmer. Cook for 30 to 40 minutes, stirring occasionally and crushing the tomatoes with the back of a large spoon as they soften. Carefully pour the sauce into a food processor. Puree and return to the pan. Keep warm over low heat.
2. Generously brush or spray the salmon fillets with olive oil; season with salt and pepper to taste. Grill the fillets, flesh side down, over Direct Medium heat until you can lift them off the grate with tongs without sticking, 7 to 8 minutes. Turn the fillets and finish cooking them, skin side down, for 2 to 3 minutes. Slip a spatula between the skin and flesh, and transfer the fillets to serving plates. Serve warm with the sauce.