Toast the 2 split English muffins until lightly golden.
Coat a medium nonstick skillet with cooking spray and heat over medium. Add the 1 cup spinach and cook for 1 minute, until wilted. Divide between the muffin bottoms.
Whisk the 4 eggs with the 1/4 tsp salt and 1/8 tsp pepper.
Return the skillet to medium-low heat and coat again with cooking spray. Add the eggs and cook for 2–3 minutes, folding gently, until set with no liquid egg remaining.
Divide the eggs over the spinach and top each sandwich with 1 cheddar slice. Cover the skillet or microwave briefly until the cheese melts.
Add the sliced tomato, 1/2 sliced avocado, and optional hot sauce. Top with the muffin tops and serve.
