Wow, you’re on the ball!
One Lent, hubby and I ate Ramen noodles for supper every friday (we split one package). We’re not really Ramen fans, so it was penitential. We’d go to Stations of the Cross and smell that delicious fish frying, and our stomachs were growling! But we had already eaten our little bowls of Ramen noodles for the evening

(we eat meatless meals on Fridays year-round, so we wanted to do something “extra” for Lent)
How about breakfast for dinner? Omelets with some chopped veggies inside, toast, and fruit?
Quesadillas!

I like them filled with fresh chopped tomatoes.
I made up a recipe a couple of nights ago–a southwestern quiche! I just took a generic quiche recipe to get the cooking times and basics, and added salsa and black beans (and I think something else, but my brain is failing me), and topped with shredded quesadilla cheese.
Of course you can take many meals traditionally served with chicken and substitute the fish of your choice (or shrimp). Last year there was a thread on here about slow cooker recipes, and someone made tilapia stew using it. I often make chicken stew in my slow cooker, so sometimes on Fridays I substitute the fish for chicken and reduce the cooking time a bit.
Hubby loves to make salmon burgers. Just like regular burgers, but using either salmon filets or canned salmon (mix an egg in and then cook like you would a hamburger patty) instead of the ground beef. Yum!!
Mac-n-cheese, as someone else mentioned–add some salsa, cooked chopped veggies of your choice, and baked/black beans, and there you have a rather tasty main course.
You could also make a salad with canned shrimp. That’s usually a side dish in our family, but it could do for dinner during Lent.
I am just wondering what lobster thermidor has to do with Lent, though…

The only penitential thing about that would be the complicated preparation

That, and serving it piping hot and burning your mouth on it, ha ha!