Preheat the oven to 190ºC. Spread the pecans in a shallow baking pan and roast in the oven until fragrant, 10 to 12 minutes, stirring occasionally. Let cool completely. Finely chop the pecans.
In a medium bowl fold all the butter ingredients, including ⅛ teaspoon of black pepper, with a rubber spatula until incorporated. Place the mixture on a piece of plastic wrap and form into a log. Chill until firm enough to slice, 20 minutes in the freezer or 45 minutes in the refrigerator.
Prepare the grill for indirect cooking over medium heat (180°C to 230°C).
In a large bowl whisk 2 tablespoons of oil with the granulated garlic, ¾ teaspoon of salt and ¼ teaspoon of pepper. Add the sweet potatoes and turn to coat evenly. Grill the potatoes, cut-side down, over indirect medium heat, with the lid closed, until they start to soften, about 30 minutes, turning once.
Adjust the grill to direct low heat (120°C to180°C) on one side and direct high heat (180°C to 230°C) on the other side. Brush the sweet potatoes with oil and then grill, cut-side up, over direct low heat, with the lid closed, until fork-tender, browned and crisp on the top, 20 to 25 minutes.
Brush the steaks with 1 tablespoon of oil and season evenly with ¾ teaspoon of salt and ½ teaspoon of pepper. Grill the steaks over direct high heat, with the lid closed, until cooked to your desired doneness, 6 to 8 minutes for medium rare, turning once.
Remove the steaks from the grill and let rest for 5 minutes. Top each steak and the sweet potatoes with a slice or two of butter. Serve warm.