Yep. Looks like BER. For some reason San Marzano/Roma type tomatoes seem to be more susceptible (at least IMO...YMMV).

Typically it is because the plant is having difficulty absorbing nutrients (mainly calcium) and can be caused by watering issues. I would mulch to help retain your moisture levels for sure. Many say that you don't need to amend your soil, however adding a calcium supplement of some kind I don't think would hurt Again, just my opinion and many say you don't need too. The few times I have had BER in the past I did...but if you read on here it is probably like putting a band aid on a non existent boo-boo, just made me feel better and didn't actually do anything. However, it did eventually go away. Most plants grow out of it once you get your watering down.

BER is a classic tomato growing problem.

There are a lot of fiction and fact about how to prevent/treat it .

I won't get into it .

Sey