1. Place 2 diced ripe avocados in a medium bowl; fold in 1/3 cup chopped red onion, 3 tbsp chopped cilantro, 1 tbsp lime juice and 1/8 tsp each salt and pepper. Line 4 plates with red leafy lettuce. On each plate arrange 2 slices roast beef, 2 slices pepper Jack cheese and a quarter of the avocado mixture. Serve with 1 tbsp reduced-fat ranch dressing.