Vegetables feel the pain when they are exposed to bad stimuli. Just because you cannot measure it does not mean that they do not experience pain. Here's the definition from Encyclopedia Britannica.
a complex experience consisting of a physiological and emotional response to a noxious stimulus. Pain is a warning mechanism that protects an organism by influencing it to withdraw from harmful stimuli; it is primarily associated with injury or the threat of injury.
heat, lack of water, sunlight etc. are all necessary for a plant life and the suitable application or withdrawal of it will show responses in planets which can arguably be classified as pain. But before you get excited about this, remember the Black Swan Theory. Nobody thought that black swans existed till the 17th century....
So, have your meat and 2 veg, you cannot win :)