It is no different to training/lifting on a proper diet: the only difference being taste. I will leave you to think about which one is better/worse.
Practically, there are certain things you have to bear in mind...
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creatine intake. Whilst I know this is an exceptionally powerful steroid that is present in all meat (mostly red meat) it is completely absent from a vegetarian diet unless supplemented. Being a very powerful steroid, it will help you get swole more effectively, but deficiencies (as caused by non-meat eating) cause deficits in working memory. So supplement it and profit from brain gains, too.
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prevalence of starchy foods. Whilst slightly easier for vegetarians than vegans (whoopee for dairy!

) beans, pulses and other stuff like that are quite high in starchy carbs which may or may not be desired. Make sure you balance your carb vs. fat vs. protein intakes accordingly. Not a problem is you do.
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grow some balls. Seriously? You let your missus dictate your diet? GTFO and MTFU.