Step 1Heat the oven to 325 degrees. Place the salmon in a shallow baking dish that fits it with at least 1 inch around all sides. Rub the fillet on the top and bottom with some olive oil then season with salt and pepper.
Step 2In a blender, puree the ¼ cup olive oil with the red onion, garlic, tomatoes and chile. Season the sauce with salt and pepper, then pour it over the salmon to cover completely.
Step 3Bake until the salmon is opaque on the outside and an instant-read thermometer inserted into the thickest part of the fillet reads 120 degrees for medium doneness, 30 to 45 minutes depending on the thickness of the fillet (if you want your salmon just cooked through, take it to 130 degrees).
Step 4Remove the pan from the oven and let the salmon rest for 5 minutes. Sprinkle with parsley, if you like, and serve family-style, straight from the baking dish with the side of your choice.