Preheat a grill. Skewer the shrimp, with zucchini slices ribboned in between each piece. Stir together the olive oil, pepper flakes, mint, and salt in a glass casserole. Lay in the skewers, cover, and refrigerate for a few hours to marinate, turning once or thrice. Cook on the grill until the shrimp are pink and the zucchini is striped with grill marks, 3 to 5 minutes per side.