For tahini sauce:

1/2 cup tahini (Middle Eastern sesame paste), well-stirred
1 clove garlic, germ removed and clove crushed with back of knife
2 teaspoons fresh lemon juice (from 1 small lemon)
1/2 teaspoon extra-virgin olive oil
1 teaspoon fine sea salt
3/4 teaspoon ground white pepper

For tempeh:
4 (4-ounce) pieces soy tempeh

For orange dressing:
1 cup freshly squeezed orange juice (from 2 medium oranges)
3 tablespoons plus 1 1/2 teaspoons white wine vinegar
1/2 cup extra-virgin olive oil
2 drops orange oil*
1 teaspoon fine sea salt
1/2 teaspoon ground white pepper

To grill and serve:
Olive oil (for brushing)
2 heads radicchio, cut into eighths through core, with some core still attached to each piece
1/4 cup (loosely packed) fresh flat-leaf parsley, coarsely chopped
2 firm-ripe avocados, peeled and cut into wedges
3 tablespoons fresh lemon juice (from 1 medium lemon)
*Available at specialty foods shops. If unavailable, use 1 tablespoon finely grated orange zest. Do not substitute orange flower water.