Preheat the oven to 390°F/200°C and line a baking pan with baking paper.
Heat the butter in a skillet and sauté the chicken thighs for 4-5 minutes on each side until golden brown.
In the meantime make the pesto: In a food processor or blender process the Parmesan cheese, basil with the olive oil, sunflower seeds, garlic and a bit of salt and pepper to taste.
Transfer the chicken thighs in the prepared baking pan and add a layer of pesto on each thigh, followed by a tomato slice and topped with mozzarella on each piece of chicken.
Bake for 25-30 minutes in the preheat oven until the chicken is completely cooked through and the cheese is golden brown and bubbly.