Preheat the oven to 300 degrees . In a small bowl, combine 2 tablespoons olive oil and the ginger; brush on the baguette slices. Transfer to a baking sheet and bake until crispy, about 15 minutes.
Meanwhile, preheat a grill or grill pan to medium-high. Grill the sausages until cooked through, about 15 minutes. Drizzle the onion wedges with the balsamic vinegar; grill until softened and charred, about 4 minutes on each side.
In a medium bowl, add the greens, the remaining 3 tablespoons olive oil and the cider vinegar; toss. Season with salt and pepper. Divide the salad among 4 plates and top with the sausages and onions. Serve with the crostini.