Healthy foods for safe weight gain/bulking?

Hi there! I’m a fairly small gal and I need some advice on a bit of weight gain. I’d still be in my healthy BMI if I put on another 15lbs.

Any advice on gaining weight?

Please don’t say to “eat more”. I eat quite a lot! I think I just need better food advice.

I do muscle building exercises at the gym but I shed weight then.

Can’t drink protein shakes! Thanks