While pasta is simmering, set a frying pan over medium heat. Add and melt 1 tablespoon butter or oil. Saute finely chopped onion and peppers until onion is translucent.
Add greens and cover pan. Reduce heat to low and cook until greens are wilted.
When macaroni and cheese is done, stir in vegetables.
EASY VERSION: Skip the onion and peppers. Instead, toss the chopped greens directly into the pasta as it boils and then simmers, cooking both simultaneously.
The One with Greens https://www.cheapskatecook.com/modified-macaroni-cheese-4-ways/