Ticklish my GF is going through exactly the same with her toddler DD.

She cuts the veges into shaped with a fancy decorating knife and cookie cutters and she found that she will eat sandwiches and muffins. So she hides veges in them by making pinwheels (flat bread lined with veges etc and rolled up) or pocket breads and grated veges in "rainbow muffins". Needless to say no toddler ever starved to death so try not to beat yourself up - he's learning to push mummy's buttons

As for food out of a jar - maybe it's the texture he prefers?

Not sure when they grow out of it tho! Sorry!

Have a good day!