Try foods that you know he likes in the jar, but in the table food form. Peas, sweet potatoes, soft green beans, canned asparagus, cooked carrots, soft fruits, smashed avocados (they have the good fat that he needs for brain development), etc.
If you want to introduce something new, you can start by mixing some into a baby food he
already likes and then gradually increase the proportion of new food and decrease the old food. It can take up to 12 times of introducing a new food before some kids will get used to it. So, be persistent and keep trying new foods often, along with his usuals.
Many babies have a hard transition from baby food to table food but it usually just takes time. My niece is almost 15 months and is still working on that transition. She is just very picky and preferred dry table food to wet ones.
You mentioned chicken nuggets... they are pretty unhealthy and have lots of preservatives and additives usually. Once he has enough teeth, you could just boil some chicken and tear it into pieces. I would stay as far away as possible from highly processed foods. Your little guy's body is growing so quickly and really absorbs anything he eats, so adding all those chemicals and unhealthy additives really has an impact on his little body. There are usually good alternatives to nuggets and similar foods in the health food section at a grocery store. Remember, fresh, all natural food will be better for him, and what he gets used to eating now, is what he will be used to eating when he gets older. A great book to read is "If It's Not Food, Don't Eat It" by Kelly Hayford, C.N.C. It is easy to read and you could find it cheap on Amazon.com or at the library. Very entertaining and really helps with ideas for eating fresh, whole, and natural foods in a way that is actually do-able and not too complicated.
Also here are two good websites:
http://www.askdrsears.com/html/3/T030800.asp "Feeding Toddlers: 17 Tips for Pleasing the Picky Eater" It has good ideas for introducing new, healthy foods to toddlers.
and
http://www.askdrsears.com/html/4/T040200.asp "ABC's of Teaching Nutrition to Kids" I thought this one was especially good because it teaches parents how to make learning about healthy food fun for kids. It talks about how to educate kids so that they make healthy choices on their own later on and so they know which kinds of food are healthy and why. The only thing I didn't agree with was that he suggested rewards, but everything else was pretty good advice. The article talks about referring to "grow" foods for kids. You could start on some of the ideas like letting him hold some vegetables in the grocery cart and talking about the colors, letting him wash the produce at home, etc. Take some of the ideas and alter them so they are age-appropriate for your son.
Best wishes!