Prep the sausage. If using raw patties, shape and cook them in a nonstick skillet over medium heat with a little oil or spray, about 3–4 minutes per side until browned and cooked through.
If using fully cooked sausage, warm it for 2–3 minutes until hot and slightly crisp at the edges. Set aside on a plate.
Toast the bagel. Split your bagel and toast to your preferred crunch level. Lightly toasting keeps the sandwich from getting soggy and adds a nice bite.
Make the yogurt spread. In a small bowl, mix 2 tablespoons plain Greek yogurt with 1 teaspoon mustard or a few dashes of hot sauce.
Season with a pinch of salt, pepper, and garlic powder. Taste and adjust. You want a zesty, creamy spread.
Cook the eggs. For a tidy sandwich, whisk 2 eggs (or 1/2 cup egg whites) with a pinch of salt and pepper.
Pour into a lightly oiled nonstick skillet over medium-low heat. Let set, then fold into a square or flip like an omelet to cook through. This helps it stay in the bagel without spilling out.
Layer with intention. Spread the yogurt mixture on the cut sides of the toasted bagel.
Add spinach or arugula to the bottom half, then the sausage patty. Place the cooked eggs on top, then add your cheese slice so it softens against the warm egg. Add tomato, onion, or avocado if using.
Close and warm. Place the top half of the bagel on the sandwich.
If you want extra melt, return the whole sandwich to the warm skillet, cover for 1–2 minutes, and let the cheese fully melt. Press gently with a spatula.
Season and serve. Give a final crack of black pepper or a splash of hot sauce. Cut in half for easier eating and enjoy right away.