Heat oil in a dutch oven or large deep skillet over medium high heat.

Add onion and garlic, cook 1 minute.

Add celery and carrot, cook 3 minutes until soft.

Increase heat to high and add beef. Cook, breaking it up as you go, until no longer pink - 3 minutes.

Add remaining ingredients EXCEPT cheese. Stir to combine, add macaroni, then turn down to medium or medium low so it's simmering gently.

Cover, cook 8 minutes. Pasta should be just about cooked, and still nice and saucy.

Add cheddar cheese, stir. Top with mozzarella cheese.

Cover with lid, cook for a further 2 minutes.

Remove from stove. The pasta should now be cooked - tender but firm, not mushy, slick with sauce, not dried out.

Serve immediately, garnished with green onions, if using.