In a large, shallow dish, mix the mayonnaise, garlic, curry powder, chili powder, and ginger. Place the chicken in the mixture, and stir to coat. Cover, and refrigerate for 2 to 4 hours.
Preheat the grill for medium-high heat.
Discard marinade, and thread chicken pieces and mushrooms onto skewers. In a saucepan, bring the rice and water to a boil. Reduce heat to low, cover, and simmer 20 minutes, or until rice is tender.
Lightly oil the grill grate. Grill skewers, turning often, for 5 to 10 minutes, or until chicken juices run clear.
In a small bowl, toss together the tomato and onions. Serve the grilled chicken and mushrooms over rice. Top with the onions and tomatoes.
