Line a baking sheet with foil. Butter the foil; set aside. In a heavy 10-inch skillet combine walnuts, sugar, and margarine or butter. Cook over medium-high heat, shaking skillet occasionally until sugar begins to melt. Do not stir. Reduce heat to low and cook until sugar is golden brown, stirring occasionally. Remove from heat. Pour onto prepared baking sheet. Cool completely. Break into clusters. Set aside.

In a screw-top jar combine vinegar, oil, pear nectar, mustard, salt, and pepper. Cover and shake well to mix. Store in the refrigerator for up to 1 week. Shake before serving.

Halve and core pears. Thinly slice pears; brush with lemon juice to prevent browning. (This may be done up to 1 hour ahead.)

To arrange salads, line plates with salad greens. Fan pear slices atop each serving. Sprinkle with some crumbled cheese and walnuts. Drizzle with 3/4 cup of the vinaigrette (reserve the rest for another use). Makes 8 side-dish servings.

Prepare nuts; place in an airtight container. Seal, label and chill or freeze up to 1 week.