One easy and cheap way is to add TVP. The unflavored TVP adds nothing to the taste but add the protein. I have never used the flavored TVP because the only way I can find it is mail order and the freight costs more than the TVP. My frequent backpacking meal consists of Idahoan potatoes with Just Vegetables and TVP. The Just Vegetables and the unflavored TVP is easily obtained locally. My meal costs about $1.

PS: I did try the bacon bits which I believe is TVP but did not like the result.