Cover the potatoes with cold water in a large pot and bring to a boil over high heat. Reduce the heat to medium-low and cook until the potatoes are just tender when pierced with a knife, about 8-10 minutes. Drain the potatoes well and transfer to a large mixing bowl.
In a medium bowl, whisk together the olive oil, vinegar, parsley, shallot, mustard, garlic powder, and oregano. Pour the dressing over the hot potatoes and toss gently to coat. Mix in the bell peppers and season to taste with salt and pepper.
Allow the salad to stand at room temperature until cool, about 20 minutes, before serving. The salad can be refrigerated for up to 1 day. Bring to room temperature before serving.
Notes
Make It a Meal: Serve the potato salad over a bed of mixed greens (such as baby spinach and arugula). Top with flaked grilled salmon and a squeeze of lemon juice.