I'm the same as you - was 5'10" 135lbs for a long time. Decided I was too skinny about a year and a half ago and posted a thread here asking the same question. I basically followed the advice in that thread - now a lean 166-168lbs, squat 1.5x that and deadlift 2x that.
Basically drink a lot of whole milk for protein and extra calories, 1/2 gallon or so a day, and eat decent foods other than that and you'll be set if you have a decent workout routine. I recommend starting strength, none of that "workout machine" nonsense.
If you have a good blender, smoothies are an easy source of decent, raw foods. I've been making one of these a day:
-1/2-1 cup broccoli (frozen)
-1/2-1 cup spinach (frozen)
-2 cups OJ
-1/2 cup oatmeal (uncooked obviously)
-2 tablespoons olive oil
I don't necessarily recommend the eggs because putting raw eggs in stuff seems sketchy, but I've been fine so far and they taste amazing
Whey protein is good if you don't wanna drink that much milk and can't get 100-150g protein elsewhere.