In a saucepan over high heat, reduce the orange juice until it forms a syrup. Let the syrup cool slightly.
In a blender, combine the orange syrup, onion, lime juice, mustard, chile powder and vinegar. Blend for 30 seconds. With the blender running, slowly add the olive oil until the dressing emulsifies. Season to taste with salt and pepper. Pour into a squeeze bottle. May be prepared up to 1 day ahead and refrigerated. Bring to room temperature before serving.