Powerlifting is a sport based around short bursts of very heavy weight lifting. Fitness is not a key objective, and weight training sessions are usually very long in duration with long rest periods between sets. Explosive power is the main goal, and whilst a heavy body weight is an advantage, too much excess body fat can impair breathing and may be a hindrance. So whilst lean muscularity is not an objective, neither should the powerlifter carry too much fat.
A powerlifter should eat for strength and with this muscle size will come, so a meal plan is not too dissimilar to that of an off-season bodybuilder. The key to healthy quality weight gain is to eat big and eat consistently throughout the day following a structured meal plan. Powerlifters should eat six or seven meals / snacks moderately large, rather than three huge meals. Include plenty of high protein food choices, like lean meat, chicken, fish, eggs and milk; fibrous low glycaemic carbs like cereals, bread, pasta, rice and potatoes; fruit and vegetables (don't forget nuts and pulses are also good sources of protein); aswell as sources of essential fats.
Timing of meals is also important; spread the meals regularly through the day. Structure is of particular importance around training as sessions can be long in duration. Have low glycaemic carbs about 30 minutes before a workout, with a small amount of simple carbs right before and straight afterwards. It may also be useful to have protein pre-, during and immediately post workout. Protein and weight gain supplements can be useful aids to gaining size and strength, but not in place of good wholesome food.
Pre-event it would be an idea to up the portions of carbohydrate foods on the day before to help load the muscles, and nutrition for an event should be similar to that of a weight training session.
The following is a sample meal plan for one day for a powerlifter of around 230lbs (105kg) body weight to help gain strength. Rest is crucial in powerlifting, so often a powerlifter only trains two or three times per week. On non-training days, the only difference should be to workout nutrition.
As with all the meal plans this is merely a guide and must not be stuck to rigidly! Eat a variety of different meats / fish / alternatives, complex carbohydrates, fruit and vegetables every day, and drink plenty of water. Adapt the plan to suit your own needs and lifestyle according to your results and performance in the gym in order to keep the strength gains coming.