Halve the cherry tomatoes. Peel the avocado, remove the core and cut into bite-sized pieces, cut the leek into rings. Put everything together in a bowl.
Mix the balsamic vinegar, mustard and olive oil and season with salt and pepper. Mix with the contents of the bowl. Then toast the bread and cut it into bite-sized pieces. Sprinkle the salad with fresh cress and serve.
If you like, you can also add pressed garlic and fresh herbs (e.g. thyme, basil).