A healthy way to gain weight would be to simply add more calories to your diet?

Adding calories to your diet will help you to gain weight, but it will not necessarily be a healthy way to do it. It depends on the foods you eat. If you eat junk foods that have a lot of refined sugar and other unhealthy ingredients, it will not be healthy. Eating a balanced diet of healthy foods, like fruits and vegetables, meats, grains, etc., but eating more is a healthy way to gain weight. Getting exercise daily is also healthy.