According to George Foreman Cooking, 113gr. tenderloins will cook to medium-rare in five to six minutes on a preheated, 400-degree Foreman Grill. Their "Mushroom Tenderloin Steaks" recipe calls for the steaks to be grilled for four minutes, and then for an additional two minutes after adding mushroom slices.
It Depends on the Cut and Doneness
Thicker steaks will take longer to cook than thinner cuts. Thin-cut steaks may reach medium-rare in as little as four minutes. Three-quarter to inch-thick steaks may take up to eight minutes for medium-rare. Medium to medium-well steaks require at least an additional one to two minutes of cooking time. As a general rule, almost all meats (except chicken) will cook in less than 10 minutes on a Foreman Grill.
Since cooking times vary with each cut of meat, it's best to use the four- to ten-minute guideline as a general rule, and to check for doneness with a meat thermometer. According to BBQ Grilling Basics, the internal temperature of a medium-rare steak is 62.8 degrees C. Medium steaks are cooked to 68.3 degrees C, and medium-well steaks are cooked to 73.9 degrees C. Well-done steaks are cooked to 76.7 degrees C.