What is a good nutrition plan for gaining muscle?

To gain you must be-: In positive caloric balance! you need to increase your protein intake to 2 grams per 2.2 lbs of body weight. And finally an appropriate weight training program every other day, or daily if you work out opposing muscle groups. Daily for the same muscle groups does not give you time to repair!

Eat variety: Eat from all food groups, fruits, vegetables, protein, whole grains, legumes, nuts, dairy. Eat a balanced meal- 20% protein, 60% complex carbohydrates and 20% from healthy fats like avocado, olive oil and polyunsaturated. To gain muscles, you need to challenge them with resistance training AND diet as suggested above- Good Luck to you.