D.W.
I have the Sneaky Chef cookbook and it has great ideas for hiding veggies in foods. That being said, I would hide the veggies and continue to offer them on his plate as well. That way he gets them in foods he'll eat but continues to see them on his plate at each meal thus building healthy eating habits. And kids go thru cycles. My daughter (also 21 months) was champ veggie eater then started spitting almost every one out and now she's back to eating them again.
As far as the potty training you have to wait until they show interest. My daughter has been training since she was 17 months but she was very interested, would tell me if she peed or poo'd so I got her a potty and let her lead the way. We are basically diaper free at home except for nap and night time. They have to do it in their own time but follow the lead they give you when they show interest. I fall into the not a fan of pull-ups! Just more expensive diapers. I never made the connection with my kids that diapers equaled baby so they didn't fight me the times they needed a diaper while we were training. I am a big fan of bare bottom when you train. Makes them much more aware of their body. You do have to watch them closely and take them to the potty every 20 minutes or so in the beginning and yes, there will be messes but they really understand very quickly what those sensations mean!