Mediterranean Watermelon Salad

½ c thinly sliced red onion
¼ c slice green onion
1 c feta cheese, crumbled
½ c coarsely chopped black olives
1 c thinly sliced fennel bulb
½ c sliced red pepper
½ c sliced yellow pepper
¼ c chopped fresh basil
2 Tbs chopped fresh mint
4 c diced seedless watermelon

Dressing

1 Tbs balsamic vinegar
1 Tbs lemon juice
1 Tbs olive oil
¼ tsp salt
¼ tsp pepper