Rap your patty in foil then oven cook it
it will retain all the moisture. fu*k that foreman grill sh*t those close lid grills cook all the juice/fat out of everything. Which is actually the purpose of a foreman grill. Like when i use to cook baked chicken I would line a glass thing with foil put a lil water in it chop some onions up put seasonings in it. The put the chicken in with it and foil the foil to cover it but still leave it open just a little. But when its done. All the flavors even the juice from the meat will be in the water which will kinda turn to a light gravy.