Preheat the oven to 400°F.

Line a baking sheet with parchment paper.

Gently pat salmon fillets dry with paper towels. Place on the baking sheet, skin side down.

Place the butter in a small microwave-safe bowl. Microwave on high until melted, about 20 seconds.

Place the paprika, thyme leaves, oregano, parsley, garlic powder, onion powder, cumin, cayenne pepper, sugar, salt, and black pepper in the bowl with the butter. Stir with a fork until a thick paste forms.

Using a spoon and clean hands, rub a scant teaspoon of the spice mixture evenly over the top of each salmon fillet.

Cut the lemon in half. Squeeze the juice of one half evenly over the fillets. Reserve the other half for serving.

Bake the salmon on middle rack of oven until it flakes easily with a fork, 12-15 minutes.

Check to see that salmon is done. Remove from oven or add time as needed.

Squeeze the reserved lemon over the fillets and serve immediately. Refrigerate leftovers in an airtight container for up to two days.