To make tortillas, melt butter in a large skillet over medium-high heat. Crack eggs into skillet, and gently break each yolk. Cook until eggs are set and flip. Season with salt and pepper, then place a slice of cheese on each egg and cook until melted. Remove eggs from skillet and set aside.

Add a corn tortilla to hot skillet and place a cooked egg on top. Layer on sliced tomatoes and spinach leaves, then top with another corn tortilla. Flip the tortilla and cook until veggies are softened and tortillas are browned on both sides, flipping a couple times as necessary. Repeat with remaining egg and tortillas.

Cut tortilla into triangles and serve with salsa and avocado slices.