Cut a slit lengthwise through each hot dog, cutting to, but not through, other side. Place hot dogs, flat sides down, in a skillet, and cook 2 minutes on each side or until browned. Drain hot dogs on paper towels.
Stir together mayonnaise and mustard; spread evenly on hamburger bun halves. Place 1 hot dog on bottom half of each bun; top each evenly with tomato, onion, lettuce, and remaining bun halves.