Melt the butter in a skillet placed over a medium-high heat.
Add the onions and cook until soft, about 4 to 5 minutes.
Add the zucchini and yellow squash to the skillet. Season to taste, cook for 5 to 7 minutes, and remove from the heat.
Grill the tomato on a grill pan or simply sear in a hot skillet, and set aside.
Bring a medium saucepan filled with water to a boil, and add the apple cider vinegar.
Crack the egg into the water and allow it to swirl around in the water until the egg begins to set, about 1 or 2 minutes.
Place the vegetables in a bowl and set the eggs on top. Lay the tomato on the side.
Sprinkle the eggs with some extra salt and pepper and serve.