Here's are a couple of simple chicken preps for the GF (or any) grill.

Slice the peel of a lemon into strips. Coat the chicken lightly with olive oil, salt and pepper to taste, and lay the lemon zest on the pieces. Cover tightly or put in zip lock bags and let sit (in fridge if done more than an hour ahead.) Cook with the zest still on (scrape off to serve if you wish.) Boneless chicken breasts or, my favorite, boneless chicken thighs, cook on the PRE-heated GF grill in about 4 minutes depending on their thickness.

Or you can brine them, which I guess is a form of marinating. You make a very strong brine solution: for example, for 2-4 boneless chicken pieces use 1 Tablespoon kosher salt (or about half that if using regular table salt), and 1 Tablespoon sugar dissolved in 1 cup water, or for large amounts use about 3/4 cup each sugar and kosher salt and a quart of water. Put chicken pieces in a zip lock bag and refrigerate in the brine for 30 minutes to a couple of hours. Then RINSE and pat dry and grill a few minutes. (You want to rinse any sugar off the surface, but you will find the brine has penetrated the meat and makes it flavorful and juicy.)

If you want sauces for grilled chicken I would put them on after cooking. Most marinades, salad dressings etc contain components which will carmelize or burn on any grill and are best wiped off before cooking, and re-applied if you wish during just the last moments of cooking. That would be difficult to do on a GF type grill. So I would wipe well before GF-ing and serve your sauce on the side.