Grill the sliced onions and sliced mushrooms in a grill basket or skillet, 5-10 minutes, or until begin to brown. Toss or stir a few times.
Spread the mustard on the bread and once the onions and mushrooms are done, begin to assemble the panini.
Bread 1/2 slice Swiss turkey meat onions/mushrooms 1/2 slice Swiss bread
Place on the grill over indirect heat and press down with brick or other heavy object. Grill for 4-5 minutes per side.
Prepare fresh fruit for side dish.
Serve Turkey, Mushroom, Onion and Swiss Panini with fresh fruit.