6 medium Yukon Gold potatoes, halved lengthwise
1/4 cup olive oil, divided
1 teaspoon Dijon mustard
2 tablespoons red wine vinegar
2 tablespoons chopped fresh oregano leaves
1 tablespoon coarsely chopped capers
1/2 teaspoon red chile flakes
2 teaspoons minced oil-packed anchovies
1/2 cup pitted oil-cured olives
1 1/2 cups halved cherry tomatoes
1/2 cup flat-leaf parsley leaves
Heat grill to medium (350° to 450°) with an area left unheated for indirect heat. Toss potatoes in 1 tbsp. oil; grill flat side down until marks appear, 8 minutes. Turn over, moving to indirect area. Cook until tender, 10 minutes. Let cool, then cut into chunks.
Whisk remaining 3 tbsp. oil, mustard, vinegar, oregano, capers, chile flakes, and anchovies in a large bowl. Gently mix in remaining ingredients.