My daughter went through a phase of doing this, she stopped after a few weeks of getting her teeth, I think she was just adjusting to eating with her teeth and it took some time to figure out. I know it can be stressful, when my daughter was doing this I cut her food up in to bite size pieces that she wouldn’t choke on but could still chew! I do BLW and her favourite food is cheese & spinach quesadillas or curry with rice
Tbh I just keep giving her the food in finger pieces and just say chew chew while exaggerating the motion. Their gag reflex is still forward so just let them experiment. I do sweet potato wedges, quesdillas, strawberry halves, pear slices, pasta twirls. She'll try it all and I just eat with her chatting.
If he has pincer grip you can start to give smaller pieces- my son is much better with smaller bits now he can pick them up. Solid starts is helping to Show you how
Imitation. Show them how to chew, sit with him and pull chewing faces. We are at 2 meals and will go to three meals next month. Her favourite meal seems to be spinach and cheese muffins. Also a daal with her spoon was a hit.