Preheat oven (electric cooker: 200 °C/circulating air: 180 °C/gas: see manufacturer). Line a tray with baking paper. Wash beetroot and sweet potatoes thoroughly, cut the sweet potatoes into slices, cut beetroot in half. Mix 5 tbsp vinegar, 3 tbsp oil and agave syrup and season with 1⁄4 tsp salt and pepper. Mix the sweet potatoes and beetroot with half of the marinade and spread on the baking tray. Bake in a hot oven for about 35 minutes.
Rinse the lentils, boil them in about 1 l water for about 25 minutes. Peel and finely dice the onion. Heat 2 tablespoons of oil in a saucepan. Sauté onion in it, sprinkle with 1 tbsp. sugar, caramelise slightly and deglaze with 3 tbsp. vinegar and 100 ml water. Cook until the caramel has dissolved. Drain the lentils and add to the onions. Season strongly with salt and pepper and let cool off.
For the hummus, rinse and drain the chickpeas. Wash the herbs and shake dry, pluck the leaves and chop them. Peel and chop the garlic. Puree everything with lemon juice, 1 tablespoon of oil and tahini. Season to taste with salt and cumin.
Clean and wash the salad, shake dry and cut in half lengthwise. Fry in 1 tablespoon of hot oil all around for about 2 minutes, season with salt. Arrange lentils, hummus, vegetables and salad.