Defrost the spinach. Rinse the lentils in a sieve and boil in 1 l water. Cook over low to medium heat for about 40 minutes until soft. Drain.
Preheat oven (electric cooker: 200 °C/circulating air: 180 °C/gas: see manufacturer). Line a baking tray with baking paper. Grate cheese finely. Squeeze the spinach very well, then chop finely. Mix well spinach, lentils, cheese, lemon juice and zest, flour, egg and Sriracha. Season with 2 tsp salt, 1⁄2 tsp pepper, 1 pinch of sugar and 3 tsp oregano. Form approx. 16 meatballs from the mixture and place on a baking tray. Bake in a hot oven for about 20 minutes until golden brown, turning once if necessary.
In the meantime clean and wash the zucchini, cut them into quarters lengthwise and cut them diagonally into pieces. Heat the oil in a large grill pan or frying pan. Fry the zucchini in it all around for about 4 minutes and take it out. Wash and halve the tomatoes. Wash the mint, shake dry and pluck off the leaves. Mix everything and season with salt and pepper. Season yoghurt with salt and mix with the salad. Arrange meatballs and salad, add lemon and sriracha to taste.