In a 10-inch cast-iron skillet cook bacon over medium heat until crisp. Remove bacon, and, let drain on paper towels, reserving drippings in skillet.
Gently crack egg into skillet; cover and fry until yolk is set 3 to 4 minutes. Sprinkle egg with salt and pepper to taste; remove from skillet.
Spread honey mustard on one side of each bread slice; add to skillet mustard side up. Cook until bottom of bread is browned about 2 minutes. Remove 1 bread slice from skillet. Place cheese over honey mustard on bread slice in skillet.
Broil on middle rack of oven until cheese is melted about 1 minute. Top with tomato slices; sprinkle with salt and pepper to taste. Add eggs bacon, and remaining bread slice. Serve immediately.
Recipe by Southern Cast Iron at https://www.southerncastiron.com/tomato-breakfast-sandwich/