Stir the paprika, sugar and onion powder together in a bowl and set aside.
In a small bowl, using a rubber spatula, combine the oregano, scallions, butter, barbeque seasoning, orange zest, 1/4 teaspoon salt and cayenne pepper. Spoon the seasoned butter onto a piece of plastic wrap. Using the plastic wrap as a shield for your hands, shape the butter into a log, wrapping it in the plastic, and refrigerate for at least 30 minutes.
Heat a grill to medium-high.
Brush the fish fillets on both sides with olive oil and season with salt and pepper. Grill the halibut fillets until the center of the fish is opaque and firm, about 4 minutes per side.
Brush the asparagus with some more oil and season the stalks with salt and pepper. Grill the spears until they are tender, turning them once, about 6 minutes total.
Transfer the fish and asparagus to serving plates. Spread a generous tablespoon of the barbeque butter over the fish. Serve the remaining butter alongside the fish, if desired.