Heat Panini grill or counter top grill on medium heat. Cut focaccia bread into two pieces; split each piece in half. Stir together Ranch dressing and mustard in small bowl. Spread mixture onto cut sides of each piece of focaccia.
Divide turkey, tomato, onion and Wisconsin Sharp Cheddar cheese slices on bottom half of each sandwich. Top with top slice of focaccia.
Grill sandwiches 4-5 minutes or until cheese is melted and sandwich is toasted.