Cut melon half into 1/2-in. rings. Cut rings with a 1-1/2-in. star-shaped cookie cutter or into 1-in. pieces; place in a bowl. Add spinach, ham, onion and grapes. Chill for at least 2 hours. Place sugar, orange juice, vinegar, onion, orange zest and pepper in a blender; cover and blend until smooth. With blender running, gradually add oil until slightly thickened. Stir in poppy seeds. Cover and chill. Just before serving, pour dressing over salad and toss. Top with pecans.