How to Make It
Preheat grill to medium (350°F to 400°F).
Thread 3 shrimp, 3 peppers, and 4 mushroom halves alternately onto each of 8 (8-inch) skewers; coat skewers with cooking spray, and sprinkle with salt and black pepper. Add skewers to grill; cook 2 to 3 minutes on each side or until shrimp are pink and peppers are lightly charred. Place skewers on a platter.
Heat rice according to package directions. Combine mayonnaise (if using) and Sriracha in a small bowl. Serve sauce with skewers, rice, and lime wedges, if desired.