If you've never made a lentil salad, get to work right away. After all, it is difficult to overestimate this dish: it can be eaten warm or cold, as an independent dish or served as a side dish to poultry, fish or meat.
Preheat oven to 175°C. Line a baking sheet with parchment. Cut off the top of the head of garlic, pour over the slice with 1 tsp. olive oil and wrap in foil.
Cut the tomatoes in half, peel the onion and cut into rings. Place the vegetables on a baking sheet, season with salt, pepper and drizzle with olive oil. Put the garlic next to it and put it in the oven for 30 minutes.
Meanwhile, bring the broth to a boil. Add lentils and reduce heat. Simmer over low heat for 30-40 minutes until tender.
Remove the baking sheet from the oven, carefully unwrap the garlic and let it cool. Gently squeeze out the cloves and mash them with a fork into a paste.
Dice bell peppers and celery. Finely chop the parsley.
Drain the lentils in a colander and transfer to a bowl. Add garlic, tomatoes, onion, celery and red pepper. For dressing, mix 2 tbsp. l. olive oil, lemon juice and chili flakes, salt and pepper. Drizzle dressing over salad, sprinkle with parsley, toss and serve.