For a Monday to Friday meal you can steam just one variety of vegetable and serve it before the soft-shell crabs. For a more elegant meal steam different vegetables (for their different colors) just until they are al dente; pat dry and set aside.
To make the vinaigrette: In a blender or food processor, puree the red peppers, mustard, garlic, vinegar, olive, hazelnut and vegetable oils. Season to taste with salt and pepper. To serve, ladle some pepper vinaigrette on a plate; pose vegetables (or vegetables) in an attractive pattern over the top.