In a large bowl combine 2 Tbsp. of the oil, 3/4 tsp. of the allspice, 1/4 tsp. of each of the salt and black pepper. Add sweet potatoes and toss to coat. Grill on the rack of a covered grill directly over medium heat 10 minutes on each side or until tender.
Meanwhile, in the same bowl whisk together the remaining olive oil, vinegar, 1 tsp. of the allspice, remaining 1/4 tsp. of each salt and black pepper. Pour over grilled sweet potatoes, thinly sliced pears, and sliced green onions; toss to coat.