Boil potatoes over the fire, grilled scallions, and other fresh flavors make for a delicious side potato salad.
In a jar with a lid, add 1/3 cup oil, the parsley, shallot, capers, and tarragon. Zest the lemon into the jar. Cover and shake the dressing base until blended; season with salt and pepper. Refrigerate the dressing base and the zested lemon separately. (The lemon will get juiced at the campsite.)
At the Campsite
Build a campfire; set a grill grate on top. Place the potatoes in a saucepan; cover with an inch of water. Salt the water generously and bring to a boil on the grill grate. Cook the potatoes just until tender, about 10 minutes, then drain. When the potatoes are cool enough to handle, cut them in half. In a large bowl, toss the potatoes with 2 tbsp. oil; season with salt and pepper. Grill the potatoes until grill marks form, 4 to 5 minutes per side.
In the same large bowl, toss the haricots verts, scallions, and the remaining 2 tbsp. oil; season. Transfer to a grill pan and place on the grill grate. Grill, tossing occasionally, until the vegetables are tender and charred in spots, about 5 minutes. Chop the scallions.
Cut the zested lemon in half and squeeze the juice into the dressing base. Add the Dijon and garlic. Cover and shake until blended. In the large bowl, toss the potatoes, haricots verts, scallions, and the dressing; season.