Problem area, anyone with defined abs that can give advice with this?

Any advice how to get more firm and defined abs? Any special food or exercise i can try to get results "easier" or quicker? I know it takes time, i dont expect anything drastic to happen within a month.

I eat pretty health, i eat healthier than anyone i know actually. I don't eat dairy and i barely eat bread, kakes or anything thats full of wheat and gluten. I only eat sweets once a week, and even then its rarely a lot. I drink just a little alcohol, maybe 1-2 times a month. I dont eat junk food, and even if i do its like 5 times a year, maybe.

I work out in general 3 times a week, and i mostly do weight lifting. When its good weather i will run intervall up a mountain. im not sure how hight it is, but people normally bring food and water to just walk up to the top.

And if it's bad weather i will run interval on a treadmill, but only for like 17 min. I have well defined legs, almost a bubble butt ( would have one if i actually was bothered to do squats), i have a 27,5 inch waist, i have big boobs and big arms (genetics). But whenever i gain or loose "a lot" of weight (like 3-4 kg) i normally notice on my stomach. So it's obviously my problem area. When i was 13 i ha a very flat stomach and defined abs, and i would love to be something similar now, without going crazy with dieting etc.

So any that could give me some advice? is my only option extreem dieting?
Problem area, anyone with defined abs that can give advice with this?
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