I have a infrared oven. I want to use it to grill eggplant and tomato. I have no clue why restaurants can do that so good. Every time I do grill them, it just like to put them into reheat. Any advice?  
I'm going to assume that 'grill' in your sense is top heat.  If so, some recommendations:   Leave the oven door slightly ajar.  This will keep moisture from building up in the oven, and steaming the ingredients.  (gas ovens always have some venting, but they can still get a build-up of steam; electric ovens will switch off if they get too hot) Get the food as close to the heating element as you can.  That will get you the layer of char on top, that you won't get if it's 6" (15cm) or more from element.  I aim for about 1" (2.5cm) from the element, although a little bit more for thick cuts of meat.  (Steaks plumps up as they cook, and they can reach up and touch the element if you're too close)  