Pat dry room temperature salmon fillets with paper towel. Season all over with salt, pepper. Squeeze 1-2 teaspoons of lemon juice over each fillet and rub in the flavour.
Heat the olive in a large non-stick pan or skillet over medium-high heat until hot. Add salmon fillets, flesh side down, while pressing lightly so the entire surface of the flesh comes into contact with the pan. Sear, undisturbed, for 3-4 minutes until crispy and golden.
Flip and sear the other side of each fillet for TWO minutes. Then, add in the butter, chopped garlic and remaining lemon juice.
Continue to cook the salmon for a further 1-2 minutes, or until salmon reaches desired doneness, while stirring the butter and garlic around each fillet. (The butter will begin to brown slightly. YUM!) Taste test and season with salt and pepper to your tastes, and add more lemon if desired.
While salmon is cooking, combine the salsa ingredients in a bowl (not including avocado). Top each salmon fillet with the tomato salsa and avocado slices.
Drizzle each fillet with the buttery sauce and serve immediately.