Extreme

OK, first of all if you want to increase lean muscle you aren't eating enough protein. Meal 1 has no direct protein source other than milk which is a poor source IMO.

Meal 3 has tuna as a protein source and its not a good source bcos it only has 14 out of 22 amino acids.

You say meal 4 is after training, I bet its not soon enough after and there is no carbs so how do you expect to replenish your glycogen levels? You should be having a post workout shake, being diabetic you'll need to watch blood sugar levels so a lot of post workout drinks won't be suitable but I think something like our Performance Mass would be good for you as it has Fructose (low GI), Maltodextrin and Pre Germinated Barley (low GI) and whey.

You could increase your solid protein intake or go for some protein drinks, a protein blend would be best as it has a slow absorption compared to whey which could alter your blood sugar levels.

PM me if you need any advice as I'll forget to check back to the thread!