For the potatoes: Cook potatoes in generously salted water until tender. Rinse and cool on sheet pan. While potatoes are cooking, toss butternut squash in 1 tablespoon olive oil and pan sear until tender.
Prepare vinaigrette and remaining vegetables. In a large bowl, combine potatoes, vegetables, olives, scallions and herbs. Toss gently to combine. Drizzle potato mixture with enough dressing to coat potatoes and vegetables. Adjust seasoning with salt and pepper to taste. Chill or serve room temperature.
For the vinaigrette: In a blender or food processor, add shallots, garlic, harissa paste, Dijon and vinegar. Process until smooth. Slowly pour in oil while blender is running to create an emulsion. Season with salt and pepper.