Pre-heat oven to 350°.
Without separating rolls, cut each package of rolls in half horizontally; arrange bottom halves in a greased 13-inch x 9-inch baking pan.
Layer with ham, cheese and pickles; replace top halves of rolls.
Using a medium bowl and the microwave, melt butter; stir in onion and mustard.
Remove from the microwave and drizzle over rolls.
Place in pre-heated oven and bake, covered, for 10 minutes.
Remove from the oven; uncover; return to oven and bake until golden brown and heated through; 5 – 10 minutes longer.
