At least 1 hour before grilling, soak plank in enough water to cover. Place a weight on plank so it stays submerged during soaking. Grease a 9 3/8x9 3/8x2 3/8-inch disposable foil pan (poultry pan); set aside.
Cook pasta according to package directions; drain. Meanwhile, for cheese sauce, in a large saucepan melt butter over medium heat. Add onion and garlic; cook for 5 to 8 minutes or until onion is very tender and beginning to brown, stirring occasionally. Stir in flour, dry mustard, and cayenne pepper. Cook and stir for 1 minute. Gradually stir in milk. Cook and stir until thickened and bubbly. Gradually add gouda cheese and blue cheese, stirring until melted and smooth. Stir in snipped fresh or dried sage.
Transfer pasta and cheese sauce to the prepared foil pan; stir gently to coat. Sprinkle chicken with salt and pepper.
For a charcoal or gas grill, place plank on the rack of a covered grill directly over medium heat. Grill, uncovered, for 3 to 5 minutes or until plank starts to crackle and smoke. Place chicken on plank. Place foil pan on grill rack, using a baking sheet to help transfer the pan if necessary for stability. Cover and grill for 20 to 25 minutes or until chicken is no longer pink (170 degrees F) and pasta mixture is bubbly.
Slice chicken; serve with pasta mixture. If desired, sprinkle with fresh sage leaves.