Clean the orange, zest the skin, and squeeze out the juice. Mix the orange juice with the thyme and a pinch of pepper in a shallow bowl. Place the turkey fillet in this mixture and let the meat marinate for ten minutes. Meanwhile, roughly chop the hazelnuts. Toast the nuts briefly in a dry skillet until fragrant, remove them, and set aside for later.
Place a pan with a little water on the heat and bring to a boil. Steam the romanesco florets for five minutes until tender-crisp, drain, and keep warm. At the same time, heat the olive oil in a skillet over medium-high heat. Remove the turkey fillet from the marinade and fry the meat on both sides for approximately four minutes per side until golden brown and cooked through.
Arrange the warm romanesco florets over a plate and place the fried turkey fillet alongside. Finish the dish by evenly sprinkling the roasted hazelnuts and reserved orange zest over the vegetables and meat. Serve immediately.