Well. In my experience and what I've seen my friends and family do is have lots of protein, but make sure it's not too much. You should have a balanced breakfast especially if you exercise have some fruits like oranges and apples. I hope this helps I'm not an expert but I hope it helps
A breakfast rich in protein and nuts, such as eggs(especially albumen),walnuts and almonds, peanut butter, and sufficient amounts of nutritious carbohydrates such as rolled oats and whole grain breads.
Breakfast is best and impront mail of the day especially when you're hoping to gain muscles. The things which contain protein are best for breakfast to increase muscle like you can have Chicken Omlate,Nuts, Chickpea Beans, dairy products,hard boil eggs, scrambled eggs ( eggs are also great sources of protein you can have them in any form)Greek yogurt with Avocado toast and some barries is another option for healthy and delicious breakfast.
One with protein and key nutrients needed to start the day. It will need to have possibly some beans, eggs and other nutrient filled foods.