Whisk the eggs with flour. Next, whisk in the milk.
Pour the egg mixture into a 12 in. x 16 in. pan lined with parchment paper. Sprinkle the top of the eggs with sauteed veggies, ham, and 1/2 cup of the mozzarella cheese. Bake the eggs at 350°F for about 14 minutes or until the edges are nearly set.
Top omelette with the remaining cheese and bake it for an additional 2 minutes or until the cheese is melted.
Roll up the omelette while it's still hot out of the oven. Start at one of the shorter ends and peel off the parchment paper as you go. Place the omelette roll on a platter and cut it into slices.
Serve immediately and enjoy the roll while the cheese is still melty!