No donot give sambar to the pet
We shouldn't feed spicy items to the pets it's not good for their gut helath
But u can give plain idli and rice without any spices
Check the temperature and check is there any low in activity
If everything is fine then to increase appetite u can give syrup like aptiquick or liv52 before food twice daily
Labradors usually wonot have any issues with the food So check his tempature once and check the deworming history also if not dewormed then do the deworming
If you are a vegetarian, it doesn't mean that your pet should also be a vegetarian. If you are planning to give only leaves, fruits and roots to your dog, I'd suggest that you give away or sell your dog to someone who can properly feed your dog with the nutrition that they require and deserve, and buy a cow for yourself, who can eat whatever you eat.
I'm sorry if my message sounded rude, but different animals require different food. The same way you cannot make a herbivores animal like a cow to live on meat, and a tiger to live eating just grass. I hope you understand what I'm trying to convey before starving your malnutritioned dog to illness and eventually death.