Season the flank steak with oil and Creole seasoning. Marinate for 4 hours, preferably overnight.
In a large bowl, add the cantaloupe, jalapeno, blackberries, red pepper, lemon juice, parsley, cilantro and green onions. Mix well. Season with salt and pepper.
Grill the flank steak to medium rare, about 6 minutes per side. Slice the steak on a bias, against the grain. To serve, fan out a few slices on a plate. Top with summer salsa.