Chill one large mixing bowl and four large individual salad bowls. Preheat oven to 350°F and preheat charcoal or gas grill to medium-high heat. Set pecans on baking tray and place in oven for 10-15 minutes, until they're dark brown, taking care not to burn. Remove pan from oven and set aside to cool. Cut each pear in half lengthwise and remove stem, bottom and seeds. Slice each half into approximately 3/16" slices. Immediately lightly brush oil on both sides of each pear slice. Place on grill for approximately 1 minute per side. Remove from grill, place on pan, and chill in refrigerator.

Cut chilled pear slices in half lengthwise. Chop cooled pecans into approximately 1/4" x 1/4" pieces. In large chilled mixing bowl, place spinach, grilled pears, grapes, blue cheese crumbles, red onion slices, chopped roasted pecans, tomatoes and vinaigrette dressing. Toss well and portion into individual salad bowls. Garnish each salad with 1/4 of the drained Mandarin oranges.