1. Microwave butter in a 2-cup glass measuring cup at HIGH 1 1/2 to 2 minutes or until butter is brown. Remove from microwave, and immediately add minced garlic.
2. Place green beans, onion, and 3 Tbsp. water in a microwave-safe bowl. Cover bowl tightly with plastic wrap, folding back a small edge to allow steam to escape.
3. Microwave at HIGH 4 to 5 minutes or until vegetables are tender; drain. Toss together hot beans and sliced onion, brown butter mixture, and salt; sprinkle with cracked pepper.