I wouldn't say that the food cooked over the volcano is a must personally.
Considering it is packed full of coach tours it is not the most ambient of meals!
THe coach tour in the volcano field is a bit of a love or hate experience - note if you are easily car sick best give it a miss!
Personally I would do the volcano tour the pop round the corner to La Geria vineyards for lunch - 10 min drive max. Again avoid the coach tour places - try El Chupadero - we went whilst on honeymoon last year and was fantastic location.