In a large saucepan, place a steamer basket over 1 in. of water. Bring water to a boil. Place Brussels sprouts in basket. Reduce heat to maintain a simmer; steam, covered, until crisp-tender, 4-6 minutes. Cool slightly; cut each sprout in half., Cut red pepper and onion into 1-1/2-in. pieces. On 4 metal or soaked wooden skewers, alternately thread Brussels sprouts, red pepper and onion. Mix salt, garlic powder and pepper. Brush vegetables with oil; sprinkle with salt mixture. Grill, covered, over medium heat or broil 4 in. from heat until vegetables are tender, 10-12 minutes, turning occasionally.