Yes it can be a challenge when a whole food group is eliminated, but definitely doable! Honestly even for us “meat” eaters there is still a lot of creativity that needs to take place to not get bored with the same foods.
Beans are going to be your friend for protein source. When you say “mostly” vegetarian, what is it that you still eat? If In know this it will help me tell you specifically what you could eat in place of the traditional sources of protein. Tell me a little more and I can help you navigate this a little better.
Filling up on fiber rich veggies is going to be integral to your success, so eat all the veggies! Don’t get hung up on “tracking” each lettuce leaf! Veggies are generally “free” foods in my opinion, of course starchier varieties do need to be taken into account (ie: carrots), but overall enjoy with reckless abandon!
I hope your week is off to a fantastic start!