Preheat a grill or grill pan on medium heat. Season the steak on both sides with salt and pepper. Grill the steak on both sides to your desired temperature using a thermometer. (see below). Once cooked place on a cutting board to rest.
In a boiling pot of salted water, cook the broccoli for 3 - 5 minutes or until tender but still firm. Drain well and set aside. Season with salt and pepper.
Mix the cheeses with the cornstarch, tossing thoroughly to coat.
In a heavy bottomed saucepan (or fondue pot), bring the wine, garlic, and lemon juice to a simmer over medium-low heat. Add the cheese cornstarch mixture to the simmering liquid a little at a time, whisking well between each addition to ensure a thick smooth fondue. Once smooth, stir in the mustard and nutmeg.
Preheat the oven broiler on low. Lightly toast the bread cubes.
Dice the steak into bite sized pieces, arrange it on a plate with broccoli, grape tomatoes, and cubed bread. Transfer the fondue to individual bowls or into a fondue pot (if you have one). Serve with wooden skewers to dip into the fondue with.