Prepare a bowl and stir together the oil, salt, pepper, paprika, water and the balsamic vinegar and season to taste. Press the garlic or cut it into small pieces and add it to the dressing, as do the diced onions.
Carefully wash the rocket and mushrooms, cut off the stems from the rocket and chop the leaves into bite-sized pieces. Cut the mushrooms into thin slices. Cut the feta into very small cubes and add everything to the dressing.