This is pa amb tomàquet, often called pa amb, Catalunya´s traditional bread & tomato dish. It´s a model of simplicity: the bread is rubbed with garlic, then with a tomato (or sometimes brushed with tomato pulp), then olive oil is drizzled over, followed by salt.
Served at breakfast (the W Barcelona had bowls of tomato pulp on the buffet), as well as at lunch & supper, there´s no way pa amb ever tastes the same way outside of Catalunya. It needs sun-filled, super fresh tomatoes not the chilled ones that make their way to the UK.
In my opinion it´s reason enough to visit Barcelona.