Preheat a Blackstone griddle to high heat. Place a skillet with butter on one side of the griddle.
Drizzle and spread oil on the other side of the griddle. Lay down the asparagus, drizzle with oil, and season with lemon pepper. Cook, turning occasionally, until tender.
Mix fresh thyme with the melted butter and reduce the heat near the skillet.
Cut the salmon into 4 pieces. Rub oil on both sides and place skin-side-down on the griddle. Season the top with lemon pepper.
After about 3 minutes, flip the salmon. Remove the skin with a fork and season this side with lemon pepper.
Continue cooking the asparagus until done, then remove from the griddle. Cook lemon slices on the griddle for a few minutes.
Remove salmon when the internal temperature reaches around 145°F and it flakes easily. Squeeze half a lemon over the salmon.
Pour the butter and thyme mixture over the salmon fillets. Top with cooked lemon slices.
