Put the torn bread in a bowl and sprinkle it with olive oil. Turn it over, then put it in an oven heated to 220°C to crisp. Take the croûtons out when they are golden and rub them lightly with a cut clove of garlic.
Cut the ham and cheese into thick matchstick-sized pieces. Put the lettuce, spinach, herbs, ham, cheese and walnuts in a good, large salad bowl. Make the vinaigrette by stirring the mustard, salt and pepper together in a bowl and gradually adding the oil to make an emulsion. Add the lemon juice and vinegar to taste. Toss the salad (not too much) and serve, mounding it into the middle of four plates. Throw a few croûtons on top of each plateful.