I need a delicious grilled / roasted chicken recipe to go with mashed potato,...

Squeeze a lemon and infuse with tarragaon. Pour over the chicken and put the cut lemon in along with it. Roast an a little butter and when cooked, make the gravy with the juices and a little cream.
Enjoy.

One thing that makes for a great chicken is to season it marinate it overnight so the spices you use on it penetrates the meat and when it's baked you get a much more flavorful chicken. So start early and let it rest with these ingredients.
2 lemons squeezed
Salt and pepper some black and pinch of cayenne
Paprika
garlic minced
onion powder
oregano
Mix all these together you be the judge how much to use according to the size of the chicken
Wash the chicken and dry it. Rub olive oil all over the chicken. Instead of roasting it whole I cut it down the middle and roast it flat using the convection part of the oven (optional) the fan blows the heat around the chicken and it gets a beautiful brown color.
After the oil treatment then add the lemon juice and spices.
Place in a plastic bag or other container and let rest overnight.
Set the oven at 375 degrees and roast the chicken uncovered for half the time and covered the rest of the time.When it's covered change the stove setting to regular roast or bake. Usually 25 minutes per pound works fine for baking time. Move the leg and if it moves easily it's done. Check with a knife and fork around the breast where it meets the thigh. so no pink juices are flowing it should be clear. Let it rest a few minutes before slicing. Enjoy!