Place the potatoes in a large pot of lightly salted boiling water and cook until just tender. The timing will depend on the size of the potatoes but it should take about 15- 25 minutes.

Drain the potatoes in a colander and run some cold water over them.

Place them in a large bowl to cool.

While the potatoes are boiling, sauté the onions in a tablespoon of olive oil over low/medium heat for 15-20 minutes, until they are transparent and slightly caramelized.

Just before removing the onions from from the heat, add the asparagus and toss.

Cook the asparagus for just a minute or two until they are bright green and tender but crisp.

Remove the onions and asparagus from the heat and add to the bowl with the potatoes.

Add the peppers to the potato mixture.

Remove the garlic from the vinaigrette and pour just enough dressing over the vegetables to coat them.

Cover and chill.

Right before serving, add the tomatoes, fresh herbs and additional dressing and toss to coat. Season generously with salt and pepper to taste.