Sprinkle the chicken fillet with salt and pepper. Heat half a tablespoon of olive oil in a pan and cook the chicken in approximately twelve minutes until done all over. Let it rest for a moment and then slice it.
Put the spinach in a large bowl. Slice the avocado and add it.
Make a dressing from the remaining olive oil, a teaspoon of mustard, a splash of lemon juice, salt and pepper. Toss the dressing through the salad.
Distribute the cooked chicken over the salad and sprinkle the pumpkin seeds over it. Serve immediately so the spinach stays fresh.