In large skillet, sauté peppers in oil just until tender. Sprinkle with salt and pepper.
Meanwhile, in small bowl, combine butter, mustard, chives, garlic, and pepper flakes.
Cut bread into 1/2-in. (1 cm) slices, leaving slices attached at the bottom. Cut loaf through the two centre slices, separating loaf into two halves.
Cut off and discard end slices. Place each loaf on heavy-duty foil coated with cooking spray. Spread butter mixture between every other slice.
Alongside buttered slices, insert cheese, meat, and peppers, using provolone cheese and salami in one loaf and cheddar cheese and roast beef in the other.
Wrap each loaf tightly in foil; place on grill rack.
Grill, covered, over indirect medium heat for 8-10 minutes or until cheese is melted.
Using a serrated knife, separate sandwiches. Or, to bake sandwiches: Bake foil-wrapped loaves at 350°F (180°C) for 20-25 minutes or until cheese is melted.