No, chickens cannot safely eat lettuce and tomatoes at my house. I get very angry at them when they raid my garden and something violent if not fatal is likely to happen to any hen or rooster who makes a habit of eating MY 'maters'.
In fact one reason that poultry keeping for food and profit has spread so widely is because no matter where humans take up residence, chickens can eat the flora and fauna naturally found there.

In fact one reason that poultry keeping for food and profit has spread so widely is because no matter where humans take up residence, chickens can eat the flora and fauna naturally found there.