Heat a pizza maker (or a skillet). Add one teaspoon oil. Pour in the egg whites, taking care to spread them in a thin layer to cover as much surface area as possible. Cook until egg white “wrap” is slightly crisp at the edges, two to three minutes. Flip and cook one more minute. Transfer to a plate and set aside.

Add remaining two teaspoons oil to the pizza maker. Add spinach and mushrooms and cook until mushrooms are golden-brown, and spinach is no longer wet.

Transfer the spinach/mushroom mixture to the top quarter of the wrap, closest to you. Sprinkle feta on top. Add salt and pepper (feta is quite salty on its own, so be stingy with the salt). Fold the sides of the wrap over the filling and roll up burrito-style.