Preheat the oven to 200 degrees Celsius. Cut the half cauliflower into equal florets and distribute them over a baking sheet. Drizzle the vegetables with half of the olive oil and season everything with the cumin, a pinch of salt and some pepper. Toss everything together well so the florets are coated all over.
Slide the baking sheet into the oven and roast the cauliflower for 25 minutes until tender and golden brown. Meanwhile, heat the remaining olive oil in a skillet over medium-high heat. Season the chicken fillet with salt and pepper and fry the meat on both sides for about ten to twelve minutes until fully cooked through.
While the chicken is cooking, prepare the dressing in a small bowl. Squeeze the lemon and mix the juice with the tablespoon of tahini. Add a small splash of water and stir the mixture vigorously until a smooth, liquid sauce forms.
Take the roasted cauliflower from the oven and remove the cooked chicken fillet from the pan. Place the warm cauliflower florets and the meat together on a plate. Spoon the tahini dressing directly over the vegetables and chicken.