Spray the inside of a 2 litre / 2 quart casserole dish with cooking spray. Set aside.
Empty the sauce mix into a microwave safe jug or bowl. Disregard package directions and instead measure 1 1/2 cups (12 oz / 350 ml) of water. Add a small amount of that water to the sauce mix, whisk to make a smooth paste, then add the rest of the water and whisk till smooth. Cook in microwave for 2 to 3 minutes until thick, then set aside to let it thicken some more as it stands.
Trim the Brussels sprouts and wash them. Cook them until tender. 
Start heating over to 175 C / 350 F / Gas mark 4.
Transfer the cooked sprouts in a large bowl or pot. Add the cheese sauce, mix carefully until all sprouts are coated with sauce. (If the sauce got too thick, you can whisk in a bit more water.) Put in casserole dish.
Rip up the two slices of bread to make fresh bread crumbs. Put in a small bowl, season to taste with herbs of your choice such as oregano, savoury, rubbed rosemary, black pepper, etc. Add the 2 tablespoons of fat-free Italian dressing, stir to mix. Sprinkle the bread crumbs on top the Brussels sprouts, spray the top of bread crumbs lightly with 1 to 2 sprays of cooking spray (this helps them brown better for "curb" appeal.)
Bake for about 35 minutes or until piping hot and bread crumbs are golden brown.