Put the oven on pre heat with a cast iron pan inside. In a bowl add the asparagus, peppers and spring onions and toss together with the oil.
In the pan inside the oven, arrange the Asparagus and peppers and toast for ten minutes. Halfway during the cooking, add the spring onions to the pan and cook all three together. You should make just one layer of the vegetables. If you need more space you can always cook them in two batches instead of topping them over each other.
While the vegetables are in the oven, make the croutons. Put your bread in a bowl and toss it well with oil. Season it with salt and pepper according to taste. Bake the bread in a baking tray in the oven. Do it for five minutes. Sprinkle Parmesan cheese over the bread and bake for another five minutes.
Make the dressing now by whisking together its ingredients in a bowl with salt and pepper. Slice the vegetables that you had griddled earlier and add them to the dressing and toss well. Scatter the Croutons over the salad and garnish with Parmesan shavings. Serve it warm.