Steam the haricots verts for 8 minutes, and set aside.

Steam the corn for 3 minutes; cool, then slice the kernels off the cob with a sharp knife.

Sprinkle the avocado slices with the lemon juice.

For the dressing, put the mustard, salt and pepper to taste, and vinegar in a bowl, and stir well. Add both oils, and whisk well.

Put all the fruits and vegetables in a serving bowl, pour the dressing over and toss gently.