In saucepan, combine 1 cup (250 mL) water, vinegar, sugar and 1/4 tsp (1 mL) salt; simmer on medium heat until sugar is dissolved. Meanwhile, place red onion in heatproof bowl. Pour hot vinegar mixture over onion; let stand 30 min. until softened. Drain.
Meanwhile, in large bowl, whisk together vinaigrette, lime juice, cumin, pepper and remaining 1/2 tsp (2 mL) salt. Add the beans, half the radishes, jalapeno, garlic, cilantro, the reserved red onion; toss to coat. Refrigerate at least 1 hr.
Toss endive with salad. Transfer to serving platter or bowl. Sprinkle with feta cheese and remaining radishes to serve.
Bean salad can be made up to two days in advance and garnished just before serving.