If it's just a skin-peeled piece of breast meat, season with ample salt, pepper, and garlic. Treat it like a steak & grill it hot about 2 mins per side, then let it sit on the cool side of the grill about 5 more minutes. Tent loosely with foil to let it rest, then slice it against the grain.
But specklebellies are about the finest in bird fare out there. They're worth the time to pluck to get the good skin-on experience.
I pluck & gut them, then rub liberally with salt & pepper. Let it dry brine for a couple hours up to a day or so. Use a meat thermometer in the breast, and cook the bird whole in a 450° oven. When the meat thermometer hits 110°, pull the bird out and let it rest for about 15 minutes. Carve the breast out, and move the meat thermometer to a thigh. Turn the oven down to 375° and finish roasting until the thermometer reads 150°.
After the carcass is done, get a cast iron skillet good and hot. Spoon some of the grease out of the roasting dish, and sizzle the carved-off breast meat skin-side--down in the skillet. One minute, tops. Flip it, sprinkle the skin with salt, and sizzle the other side of the breast for a minute. Let it rest, and then serve everything all at once. Use the melted goose fat to dip the meat in.
It's delicious. Sounds like a lot of work, but it's really not. It's a good way to use the whole bird, and it tastes incredible. When you're done with it all, save all the bones and throw them in a pot with the carcass to make a stock.