Have you got a slow-cooker? Slo-cooked chicken casserole or similar should be pretty soft. And add fruit to make it sweet (chicken & peaches, pork & apricot etc). Then park him in front of cbeebies and shovel it in...
If we get warm weather again you could try picnicing in the garden. Might be distracting enough to get him eating. Jam sandwiches defy pulling to pieces quite well.
Nutritionally, weetabix and fruit sounds great. DD has that for breakfast and its the best meal of her day! Is your issue that he's not eating well (content) or that he's not progressing onto more adult-type food? One option is to chill out, and keep feeding him mush until all his molars are through.
What about skinless cocktail sausages? And Smiley potato faces (dd wouldn't touch potato till we found these; progressed onto roast potatoes afterwards). Thomas Tank nuggets? You can move onto less junk-type-stuff once he's got used to chewing.
The other thing that worked for dd was eating with other kids. Do you have any friends with slightly older children that you could invite round for tea?
How about sitting and eating toast with chocolate spread on, in front of him, and say "no, no, you can't have this it's only for big people" until he begs?
Sorry this is a bit disjointed, brain is having a weekend.