My daughter (now 11 months) did that at 9 months too. (But she had teeth). I immediately offered plain (cooked) vegetable pasta, cut in smaller pieces (although she's fine with it uncut now; I now have a variety of different kinds that I cook up); cut up, soft avocado pieces; and baked chicken, I pull some shreds off break it up into small pieces by hand (I buy it cooked from the grocery store, the plain not flavorings). She immediately ate it up, no issues. I then introduced: cooked ground beef (made sure no big chunks), no salt canned carrots, canned green beans (french cut, are very thin--especially if he doesn't have teeth), canned corn, steamed broccoli (pick the little florets apart into single tiny florets), blue berries, freeze dried strawberries, freeze dried peas, baby rice cakes (Yum Yum brand). The only thing she'll let me feed her (with a spoon) is yogurt.
You can try canned chicken, mushed up so there's no chunks and mixed with plain yogurt (I wouldn't do mayo yet due to egg allergy risks). Hand roll it into little balls. It shouldn't require much in regard to teeth.
Good luck! (Of course, he might be teething and that might be why he doesn't want to eat.)