Cook the red lentils in the vegetable stock for about 5 minutes until they are firm to the bite, then drain.
Mix together lemon juice and olive oil, season with sea salt and pepper, add garlic. Cut tomatoes into wedges. Mix the lukewarm lentils, chopped onion, tomatoes and cress with the dressing.
The salad can be served lukewarm or cold, I prefer it lukewarm!