オムライスって英語でなんて言うの？

I personally think that it's great to use the original names for very unique foods and then simply describe them. Of course, you have lots of great options! :D
Have a lovely day!

An omurice is a Japanese omelette made with fried rice.
This dish is usually topped with tomato sauce (ketchup).

'Omu' is an abbreviation for 'omuretsu' (omelette pronounced with a Japanese accent) and 'rice' (pronounced raisu) refers to the sweet and savory chicken rice it's filled with. This is known as 'omurice' which is a type of 'yoshoku' which means western influenced Japanese cuisine. In western terms this would be described as a omelette stuffed with rice and usually eaten with a generous squirt of tomato sauce.
"Would you like to try 'omurice'"
"What is it?"
"It's sweet and savoury rice wrapped with an omelette with a squirt of ketchup."
"OK, thanks - sounds delicious!."

An omelette or omelet is made with beaten eggs fried in oil or butter, the rice gets added inside and then the egg mixture gets folded over, to trap the filling inside.

It is called an "omelette."

----> An omelette is a type of food made by beating eggs and cooking them in a flat pan.

omelette - this is the french word for a type of fried egg dish

ketchup - this is a sugary tomato sauce

Fact: Ketchup is a common condiment or sauce that most burger joints will give you with your burger and fries in America.

An omelette is a egg that is cooked/fried on both sides. In America it's common to have an omelette as a breakfast food. It can be eaten plainly. However, people also stuff omelettes with various vegetables, cheese, or even rice. In these cases we describe the omelette by its ingredients.
Can i have one rice omelette and another plain omelette with cheese, tomatoes, and onions please?

In Japan it is called a omreis and in English it is called an omelet. They usually consist of stir fried vegetables or meat and is wrapped and fried in eggs.