I'd try having something he wants and a green veg. Say this first then that. 19months he should 'get' it

My kids first foods are vege sticks so I haven't had this problem.

But I know as they have gotten older if they are 'off' something I'll do two bowls. One with veg one with the protein. I'll give whichever bowl they aren't interested in first and the second bowl is the reward

Also try tiny amounts so he isn't overwhelmed. Better to get praise for eating everything than fighting to eat heaps

HTH