A vegetarian plate still needs a yes
Vegetarian means no egg, meat, or fish. The plate still needs a food they already eat: rice, dal, potato, fruit, bread, or beans.
The diet is the boundary
A new vegetable goes beside that food. The diet is the boundary. The familiar food is the comfort.
No egg, meat, or fish is the whole rule. You do not have to explain it further at the table.
A yes they already accept
Lentils and rice, potato, fruit, beans, or bread if wheat is fine. One of those should be a food they already eat.
Cheese and yogurt belong only if milk is fine. A milk allergy takes them off a vegetarian plate too.
Do not test the boundary
A little chicken “just to try” is a different diet. Change the saved diet in the app when the house changes, not in the middle of a bite.
The app keeps egg and chicken off while the diet is vegetarian.
A sentence you can say
“No egg, meat, or fish. Your rice is here.”