Put the bread, garlic and low-fat spread in a small heavy frying pan over a gentle heat, and toss until golden. Remove from the heat, discard the garlic and drain the croûtons on kitchen paper.
Put the rocket, coriander and parsley in a small salad bowl. Scatter the onion and croûtons over the top of the greens. Sprinkle with the vinegar, and season well with salt and pepper. Serve.