Carefully trim crust from top of bread.
Make 6 diagonal cuts at equal intervals from top of loaf almost to bottom.
Mix butter, onion, mustard, poppy seed, lemon juice and cayenne red pepper.
Reserve 3 tablespoons butter mixture.
Spread remaining butter mixture into cuts.
Alternate 2 cheese slices and 2 meat slices in each cut, allowing each to stick out slightly at top and sides of loaf.
Spread reserved butter mixture on top and sides of loaf.
(To serve immediately, see below.) Wrap in heavy-duty aluminum foil and refrigerate.
1 hour before serving, heat oven to 350°.
Place wrapped Hearty Sandwich Loaf on ungreased baking sheet; open foil.
Bake 30 minutes.
Cover loaf with foil; bake until hot, about 20 minutes.
To serve, slice through each diagonal cut between meat slice and bread.