Heat walnuts in a small nonstick skillet over medium-low heat, stirring often, 5-6 minutes or until lightly toasted and fragrant.
Remove rolls from packages. (Do not separate rolls.) Cut rolls in half horizontally, creating 1 top and 1 bottom per package. Spread preserves on cut sides of top of rolls; sprinkle with walnuts. Spread mustard mayonnaise blend on cut sides of bottom rolls; top with roast beef and cheese. Sprinkle with salt and pepper, if desirsed. Cover with top halves of rolls, preserve sides down, and wrap in aluminum foil.
Bake at 325 for 30 minutes or until cheesse is melted. Slice into individual sandwiches. Serve immediately.
To make ahead: prepare recipe as directed. do not bake. Freeze up to 1 month. Thaw overnight in refrigerator, and bake as directed.