Is my daily diet healthy?

I’m asking this because I have found recently that I have lost 5-3 lbs in a week which wouldnt be concerning because my metabolic rate is in 99th percentile but in just 5 days since I’ve started it, I would think this is fast. I’m not looking to lose* weight, In fact I would like to gain weight and muscle.

Basically I start the day with oatmeal, quite a lot, a banana and some blueberries. Lunch I usually skip or just have a burger or legumes and for dinner, I have 2 cups of legumes and chicken maybe with some blueberries. An occasional second banana. I only drink water.

Would this be considered a weight loss diet and how do you think, If I could, turn into a muscle gaining or just general health diet?

5’11, 140, 18.

Is my daily diet healthy?