Preheat oven to 300 degrees.
In a small bowl, mix together the ranch dressing and hot sauce.
Spread 8 slices of bread each with 1 teaspoon of reduced-fat butter. Flip bread over and spread inside of each slice with ½ tablespoon of ranch spread.
On 4 slices of bread, on the ranch spread, divide and place roast beef, red peppers and arugula on each. Top each with 1 slice of cheese. Place remaining bread slices on top.
Heat a large nonstick pan over medium heat. Place 2 sandwiches in pan, cover, and cook until golden brown, about 3-4 minutes. Turn over and cook covered for about 2 more minutes, until cheese is melted. Turn over and cook for 30 seconds more. Transfer to a baking pan and place in the oven to keep warm. Cook remaining sandwiches. If using a Panini or sandwich maker, both sides are cooked at once so it takes about 4 minutes total.