PLACE walnuts, arugula, dressing and crushed red pepper in food processor; cover. Pulse until mixture has paste-like consistency. Season with salt and black pepper. Transfer to bowl; cover. Refrigerate until ready to use.
FOR each serving: Grill one side of each of 2 bread slices 30 sec. or until lightly toasted. Spread 1 rounded Tbsp. of the pesto mixture onto untoasted side of each bread slice. Top 1 of the bread slices with 1-3/4 oz. of the pepper strips and 1 oz. of the onions; cover with 1 Brie slice, 2 peach slices and remaining bread slice, pesto-side down. Place in sheet pan sprayed with cooking spray.
BAKE in 350ºF-convection oven 1 to 2 min. or just until cheese begins to melt. Serve warm.