With throwing food he's exploring all new avenues and thinks its exciting, especially to see your reaction I would imagine.
Spoon feeding is going to be messy, but I would be firm and tell him you do not throw, don't laugh, or get angry - cause a reaction, cos he'll think its funny. Spoon feed with him (one spoon each) and i'm afraid its going to be practice practice practice.
Adding Lumps in though is really important, not only to stop him being fussy with food but also because the chewing helps develop his mouth muscles and jaw for talking.
What spoons are you using? Have you got toddler ones where the handles are shorter? DS finds them.so much easier to manipulate than the baby spoons.