Preparation Spray grill rack with nonstick spray. Prepare barbecue (medium-high heat). Whisk vinegar, sugar, 1/2 cup oil, mustard, and tarragon in medium bowl. Season dressing with salt and pepper. Brush cabbages and green onions with oil; sprinkle with salt and pepper. Grill cabbages until dark grill marks form, 3 to 4 minutes per side. Grill green onions until charred on 1 side, 2 to 3 minutes. Transfer vegetables to work surface. Chop green onions and cabbages; place in large bowl, discarding cores. Add dressing; toss to coat. Season slaw to taste with salt and pepper.
Preparation Spray grill rack with nonstick spray. Prepare barbecue (medium-high heat). Whisk vinegar, sugar, 1/2 cup oil, mustard, and tarragon in medium bowl. Season dressing with salt and pepper. Brush cabbages and green onions with oil; sprinkle with salt and pepper. Grill cabbages until dark grill marks form, 3 to 4 minutes per side. Grill green onions until charred on 1 side, 2 to 3 minutes. Transfer vegetables to work surface. Chop green onions and cabbages; place in large bowl, discarding cores. Add dressing; toss to coat. Season slaw to taste with salt and pepper.