Diet ?

hello guys my stats im 5'8 155lbs lean with not that much body fat.
i work out 4 days a week, for the past 10yrs and im in good health.
im 38yrs old, ive always had a problem trying to put on weight.
now at my age i notice if i do put on weight i seems not to be
lean muscle i guess cause i dont have a proper diet,
im a very healthy eater but the problems i have is trying to find the time
to eat every 2 to 3 hrs cause of my work skd, its hard workig at
the airport check in counter and trying to get in 3 meals within those 8 hrs of work. since i only get one break time.
any suggestions and can some one please post a example of
a diet that would be ideal for a mass builder with the exception
of putting on very little body fat... at the moment i eat

1st meal
8am 3eaggs
2 slice of whole weat bread

2nd meal
chicken breast
1/2 cup of white rice
1 apple

3rd meal
2 slice of chicken breast
one baked potato

4th meal
bed time
1 apple

if any one have any suggestion, will greatly apprecitate