Preheat oven to 450°F / 230°C.
Finely mince garlic and thinly slice onion.
Heat up olive oil in a nonstick skillet over medium-low heat. Add garlic and onion and cook for 20-30 minutes or until onions are caramelized, stirring occasionally.
Meanwhile, season salmon fillets generously with salt and pepper. Place salmon on a nonstick baking sheet and bake for 10-15 minutes or until salmon is cooked to your liking.
When onion is caramelized, add soy sauce and lemon juice and stir to combine. Remove from heat and keep warm.
When salmon is cooked, spoon the caramelized onion on top of salmon fillets. Sprinkle with extra black pepper if desired. Serve immediately. Enjoy!