What beer sort would pair good with lasagna, and other sorts of food with high tomato content?
What makes the taste of that beer compose good with the taste of lasagna/tomatoes?
Thinking about a tomato pasta, I get acids, strong aromas, and a lingering mouthfeel. Based on this, I would lean towards a Flanders Red or Flanders Brown / Oud Bruin, depending on the acidity of the sauce (the red for more acid, the brown for less). These beers tends toward a wine-like experience, with their own acids and richness. You won't have a lot of hop presence, which would battle the aromas of the food, and the sour characters of a Flanders Red would compliment a strong tomato sauce. Alternately, perhaps a English-style brown ale, for its low bitterness and malt profile.
Previous answers are good, I'd just add to pay attention to ABV, which is gonna be mid-high (around 6-7). As suggested here, you'd want the alcohol and the (not too much) hop to cleanse your palate, and it is maybe "easier" than the acid of sour ales or Oud Bruins.
Such opulence (...) goes well with a well structured craft beer, but with sharp "weapons" to de-grease the palate. I would suggest an amber ale, or a darker amber: caramel malts, lightly toasted - excessive roasting may in fact have to battle with ingredients such as tomatoes.(...)
Our beer, we said, must also have the ability to " clean up" the palate, perhaps with a touch of citrus fruit or herbal, with a pleasant feeling of hops. But absolutely shouldn't be too sweet. So we'd prefer a product that is dry, bitter and strong with good carbonation, since bubbles help the drinkability. As for the alcohol, it would be preferable not to exceed 6 and 7 percent
As object88 mentioned, you're gonna want a Flanders Red or Flanders Brown because they are more wine like than beer like. You're gonna want to avoid overly hoppy beers like your IPA's or even pale ales. You could probably get away with a good lager or pilsner as well. Another suggestion, if you can get your hands on it would be one of Dogfish Head's newest ancient ales, Birra Etrusca Bronze, which is a recreation of an ancient Roman beer from the Tuscan part of Italy.