Heat a non-stick skillet over medium heat and add a tablespoon of olive oil. Wait until it shimmers.

Crack a large egg into a bowl, season it with salt and pepper, and pour it into the skillet. Cook for 2-3 minutes until the whites are set but the yolk remains runny.

Toast two slices of whole grain bread until golden brown and crisp, about 4-5 minutes.

In the same skillet, add a handful of spinach and halved cherry tomatoes. Stir for 1-2 minutes until the spinach wilts.

Assemble the sandwich by spreading pesto on the toasted bread, adding sautéed vegetables, and crumbled feta on one slice.

Place the cooked egg on top, add avocado if desired, and complete the sandwich with the other slice of bread, pesto side down.

Press the sandwich in the skillet on medium heat for 1 minute on each side for extra crispiness.

Slice the sandwich in half and serve immediately while warm.