As you may know confit is a French word meaning "preserved" and usually is used to describe a slow cooking technique whereby a tough cut of fowl such as a duck leg or goose was cooked slowly in its own fat, and then sealed in this fat to protect it from decomposing, and could be cellared before refrigeration was invented, for many months without spoiling.
Confit can also be seen in the word confiture which tranlates as a preserve in the sense of a jam or jelly is preserved with extra sugar added to protect it also from spoilage.
Ian takes Roma tomatoes and cuts them in half and tosses them in olive oil, herbs and chopped garlic. Then he puts them in the oven over-night with just the pilot light left on. This allows the tomato to be cooked for ten or more hours, slowly enhancing the tomatoes sugars and making the tomato even more tomatoey.
The he takes some fresh Dungeness crabmeat and stuffs the preserved tomato, serving it on a frilly bed of spring greens, and surrounding the plate with a spring vinagrette made from extra-virgin olive oil and cooked rhubarb with citrus, and a little shaved reggiano over the top.