What You'll Need:
1 slice of hearty, whole-grain bread
1 to 2 thin slices red onion
4 to 6 thin slices cucumber
1/2 ripe avocado
Freshly ground pepper
1 slice (about 1 ounce or 28 grams) Swiss cheese
How You'll Make It:
1. Preheat the broiler.
2. Spread the bread generously with mustard. Scoop the avocado flesh from the peel with a spoon and slice lengthwise. Fan the avocado on the mustard. Arrange the onion slices and cucumber over the avocado and sprinkle lightly with salt and pepper. Top with the cheese.
3. Place under the broiler until the cheese is just melted and bubbling, about 1 minute.