Cook the rice according to package directions. Transfer the hot rice to a medium-sized bowl and add the onion, Jarlsberg cheese, garlic, and zucchini. Stir well and set aside.

In a small bowl, mix together the farmer cheese, vermouth, capers, mustard, vinegar, salt, black pepper, and cayenne pepper. Stir into the rice mixture.

Cut 1-1/2 inches off the ends of the bread, then cut the loaf into 3 large pieces. With a sharp serrated knife, remove the inner portion of each piece, leaving a 1/2 - 3/4-inch-thick shell. Reserve the inner portion of the bread for another use.

Firmly stuff each shell with the rice mixture, packing it well and smoothing the ends so they do not bulge. Wrap each shell tightly in foil and refrigerate for at least 4 hours or overnight.

When the bread rolls are cold, cut them into 1/2-inch slices with a serrated knife. Rewrap and refrigerate until ready to serve.

Arrange the canapés on a pretty platter and serve them alongside a bowl of tangy mustard.