1. Soak radicchio quarters in bowl of cold water 1 hour, placing plate on top to keep radicchio submerged. Drain, squeeze dry with clean towels, and cut each quarter into 3 1-inch sections, discarding stem portion.
2. Set steamer basket in large saucepan filled with 1 inch of water, and bring to a simmer. Place eggplant in basket, cover, and steam 1 minute. Add squash, cover, and cook 5 minutes more. Cool.
3. Soak raisins in small bowl of warm water 5 to 10 minutes. Drain, chop, and set aside.
4. Toast pine nuts in dry skillet 3 to 5 minutes, or until beginning to brown. Chop 3 Tbs. pine nuts, and leave 1 Tbs. whole. Combine pine nuts with chopped raisins.
5. Thread 1 radicchio section, 1 avocado cube, 1 squash slice, and 1 eggplant slice onto each skewer. Repeat threading so each skewer has 2 of each vegetable.
6. Heat oil in small skillet over medium heat. Add garlic, marjoram, and pinch of salt; cook 2 minutes, swirling skillet occasionally. Add balsamic vinegar, then remove from heat. Brush kebabs with oil mixture. Return pan to medium heat, add raisins and pine nuts, and cook 30 seconds to 1 minute. Set aside.
7. Heat grill to high. Grease grill grate with oil. Set kebabs on grill, adjusting eggplant and squash pieces so they touch grill as much as possible. Cook 2 to 4 minutes with lid open. Flip kebabs, and cook 2 to 4 minutes more, or until grill marks appear. Transfer to serving platter, and spoon raisin and pine nut mixture over kebabs.