Preheat oven to 375 degrees.
Coat a 9- x 13-inch baking dish with 1 teaspoon of olive oil.
Sprinkle salmon fillets with salt and pepper then arrange them in prepared baking dish. Top with onion slices and dill sprigs then drizzle with remaining olive oil and the lemon juice.
Bake salmon for 20 to 25 minutes or until internal temperature registers 145 degrees and fish flakes easily when tested with a fork.