How to Make It
In a blender, combine the vinegar with the garlic, shallot, mustard, basil, and oregano and puree. With the machine on, pour in 1/4 cup plus 2 tablespoons of the oil; season with salt and pepper.
Light a grill or preheat a grill pan. Season the pork with salt and pepper. Grill the pork over moderately high heat, turning once, until browned and cooked through, about 10 minutes. Transfer to a cutting board and let rest for 5 minutes.
Meanwhile, in a medium bowl, toss the tomatoes, onion and asparagus with the remaining 2 tablespoons of olive oil and season with salt and pepper. Grill the vegetables over moderately high heat until lightly browned, about 2 minutes for the tomatoes and 4 minutes for the onions and asparagus. Transfer to a plate.
In a large bowl, toss the mesclun with the prosciutto, grilled onion and half of the vinaigrette. Mound the salad onto plates. Thinly slice the pork and arrange it on the plates, along with grilled tomatoes and asparagus. Drizzle the pork and vegetables with the remaining vinaigrette and serve.