Preheat the oven to 350°F. Position the oven rack in the upper third of the oven (so the top of the fish will be close enough to the broiler for finishing).
Line a large rimmed baking sheet with parchment paper.
Pat the 2lbs fresh salmon dry with paper towels and place it skin-side down (if it has skin) on the prepared baking sheet.
In a small bowl, combine 1/2 tsp salt, 1/8 tsp sugar, 1/8 tsp ground black pepper, 1/8 tsp garlic powder, and 1/8 tsp paprika; mix to make the seasoning.
Evenly sprinkle the seasoning mixture over the top of the salmon.
Spread 1/3 cup mayonnaise in a thin, even layer over the seasoned top of the salmon.
Arrange the lemon slices on top of the mayonnaise-covered salmon.
Cover the baking sheet tightly with foil and bake at 350°F for 20 minutes.
Remove the foil, switch the oven to broil, and broil the salmon for about 3 minutes, watching closely, until the top is golden and slightly crisp.
Remove from the oven and let the salmon rest for a couple of minutes before serving.