First, prepare your avocado. Cut it in half, remove the pit, and scoop the flesh into a small bowl. Mash it well with a fork until smooth or chunky, depending on your preference. Season it with lemon juice, salt, black pepper, garlic powder, and chili flakes. Stir everything together.
Next, prepare the chicken breast. Slice it into three even strips. Season the strips generously with a pinch of salt and black pepper on both sides.
Slice the mushrooms. Wash and thoroughly dry the rucola. Cut two thick slices from the heirloom tomato.