3 cups of broccoli = 6 net carbs (according to fitday)
3 cups of cauliflower = 8 net carbs
3 cups of raw spinach = 1 net carb

9 cups of some of the more carby veggies and you still arent at your 20 yet. and plenty of room for eggs and cheese.

Add some spinach to your omlettes and replace lettuce with spinach in your salads (raw)
melt some cheese on top of broccoli or roast it together with some cauliflower and just toss some olive oil and spices on it or cook it with chicken thighs and let the broccoli roast in the juices/fat

You would really be eating a ton of veggies to get 20g of carbs from them, unless you were eating a lot of sugar snap peas, onions, sqush and tomatoes.

Asparagus is another veggie that is easy to overdo and mushrooms.

make sure you get these veggies in, they are super important, and it does you no added benefit to hover around 10-15g of carbs a day... you need your fiber. I stay at around 18 a day and give myself a bit of room for hidden carbs (spices etc.)