Onions are a source of a flavonoid called quercetin, known to help decrease levels of histamine related to springtime allergies. Quercetin is also available as a supplement.
1. Whisk together mayonnaise, vinegar, horseradish, and honey in a large bowl. Add cabbage and onions, stir to mix, and let stand for 10 to 15 minutes to let flavors blend.
2. While slaw marinates, cut each piece of tempeh crosswise into quarters, then cut each quarter horizontally into two thinner slices. Sprinkle tempeh pieces with tamari.
3. Heat oil in a large skillet and cook tempeh for 3 minutes on each side, until golden, turning carefully to prevent breaking. Transfer tempeh after it’s cooked to a plate and cover with another inverted plate to keep warm.
4. To assemble, arrange hot tempeh on 6 slices of bread. Top with slaw. Cover with remaining bread. Press down gently and cut in half on the diagonal. Arrange two halves on each plate, along with a pickle, and serve immediately.