Soak 4 8-in. skewers in water for 20 minute Preheat barbecue to medium. Cut 1 cauliflower into large florets. Thread about 3 florets onto each skewer. Whisk 2 tbsp lemon juice with 1 tbsp chopped fresh oregano, 1/4 tsp salt and 1/8 tsp hot-red-pepper flakes. Slowly whisk in 3 tbsp olive oil until mixed. Brush cauliflower with half of vinaigrette. Oil grill and barbecue cauliflower skewers, lid closed, until tender-crisp and grill marks form, about 6 min per side. Transfer to a platter and brush with remaining vinaigrette.